JP2857263B2 - Low-voltage uninterruptible switching device for transformer and method for switching and switching back - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-voltage uninterruptible power switching device for a transformer and a method for switching and switching back.

[0002]

2. Description of the Related Art In recent years, due to the diversification of lifestyles and the rapid progress of a highly information-oriented society, the power system, which is one of the pillars supporting them, has been increased in scale and complexity. An even higher stable supply is required. From these requests,
The construction method of the low voltage instantaneous switching method in electric power facility construction is being promoted. For example, as shown in FIG. 8, when replacing the pole transformer Trb of one of the banks A and B, the load LB of the bank B is switched to the bank A, and the replacement of the transformer LB of the bank B is performed during the construction of the bank B. Power is supplied from the bank A to the load LB of the bank, and the load LB is switched back to the bank B after the construction is completed.

[0003] As a method of switching the load LB of the B bank to the A bank, a low voltage switch LS connected to the low voltage side of the B bank automatically switches the switching unit in response to the absence of voltage on the load side. There is a method of connecting the switching switch K1 having a closing action within 10 msec), connecting the switching switch K2 having the same configuration as above to the branch point of both the A and B banks, and performing switching according to the following operation. .

In this method, first, the switching switch K1 is turned on by manual operation. The low pressure switch LS is turned off by manual operation. The switching switch K1 is turned off by manual operation. The switching switch K2 has a load LB
Side detects no voltage, and instantaneously (10 msec
), The current IA flows from the bank A to the load LB side.

The load L which has been switched to the A bank is
When returning B, the following procedure is performed. Switching switch K
2 is turned off by manual operation. Switching switch K
1 detects that the load LB side has become no voltage, turns on instantly (within 10 msec), and the current IB flows from the B bank to the load LB side. The low pressure switch LS is turned on by manual operation. The switching switch K1 is turned off by manual operation. Remove the switching switches K1 and K2.

[0006]

However, the above method has a problem that an instantaneous power failure (within 10 msec) cannot be avoided. Furthermore, since a low-voltage switch (low-voltage branch box) is required on the secondary side (low-voltage side) of the transformer, this method must be implemented in a system without a low-voltage switch (low-voltage branch box) on the low-voltage side of the transformer. There is a problem that can not be. In addition, two switching switches are required, and there is a problem in that it takes time to connect the switching switches and to remove them after the construction is completed.

As a method of avoiding an instantaneous power failure and switching the load of the bank B to the bank A, there is a loop switching method, which will not be described in detail here. This method has a problem that the loop cannot be formed if the two types of ground phases of the transformers of both banks are different.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to realize a low-voltage transformer having a completely uninterrupted power supply and requiring only one switching device. An object of the present invention is to provide an uninterruptible switching device and a switching / switchback method.

[0009]

According to a first aspect of the present invention, there is provided a low-voltage uninterruptible switching method for a transformer, comprising: an inverter circuit having a first switch; A switching device including a bypass circuit having a switch is connected between one bank and the other bank, and when switching between one bank and the other bank, first, in a state where the first switch and the second switch are opened, After the output voltage was converted to the same voltage and the same phase as the voltage of one bank on the output side by the inverter circuit, the first switch was closed, and then the primary cutout of one bank was opened. Then, the output voltage is gradually returned to the same voltage and the same phase as the voltage on the input side which is the other bank side in the inverter circuit, and after returning the voltage, the second switch Closed, it is to its gist to supply power via the bypass circuit to open the first switch on the load side of one bank from the other bank.

According to a second aspect of the present invention, there is provided a low-voltage uninterruptible power recovery method for a transformer, comprising: an inverter circuit having a first switch; and a bypass connected in parallel to the inverter circuit and having a second switch. And a switching device having a circuit connected between one bank and the other bank, and supplying power from the other bank to the load of the one bank via the bypass circuit. When switching back to the bank, the second switch is turned off, the bypass circuit is cut off, and the first switch is closed so that the voltage and the phase are the same as those of the input terminal side which is the other bank side. First, the inverter circuit is operated, and thereafter, the output voltage is gradually returned to the same voltage and the same phase as the voltage of the output terminal side, which is one bank side, by using the same inverter circuit. After returning to the output terminal side of the voltage of the click is complete, it is to that closing the primary cutout of one of the banks and the gist thereof.

A low-voltage uninterruptible switching device for a transformer according to a third aspect of the present invention includes an inverter circuit having a first switch, and a bypass circuit connected in parallel to the inverter circuit and having a second switch. And controlling the inverter circuit so that the output voltage becomes the same voltage and the same phase as the voltage on the output side bank side, and the output voltage becomes the same voltage and the same phase as the output side bank side voltage. After that, first control means for controlling the inverter circuit so as to gradually return the output voltage so that the output voltage becomes the same voltage and the same phase as the voltage of the original input terminal side; and The inverter circuit is controlled so as to have the same voltage and the same phase as the voltage on the bank side, and makes the output voltage the same voltage and the same phase as the voltage on the bank side which is the input side. And then, a second control means for controlling the inverter circuit output voltage to return gradually to become a voltage equal voltage and the phase of the output side of the bank the output voltage, the return bank changeover and bank switching Sometimes as below
Switch control for controlling a first switch and a second switch
And a low-voltage uninterruptible switching device for a transformer comprising:
You. (When switching banks) (1) When switching between one bank and the other bank,
Leave the first switch and the second switch open.
You. (2) In the inverter circuit controlled by the first control means
And the output voltage is compared with the voltage of one bank which is the output side.
Close the first switch after conversion to the same voltage and phase
Control. (3) After that, the primary cut-out of one bank
After releasing the point, the point controlled by the first control means is released.
The inverter circuit has the same voltage as the input voltage of the other bank.
After returning the output voltage to
The switch is controlled to close, and after the second switch is closed, the first
Switch is opened. (At the time of bank switching back) (1) One bank from the other bank via a bypass circuit
While power is being supplied to the bank load , the other bank
When switching back from the bank to one bank, close the first switch.
After opening the first switch, open the second switch
To shut off the bypass circuit and set the first switch
Close.

[0012]

According to the above construction, the first invention switches the one bank and the other bank by the switching device, and opens the output voltage by the inverter circuit with the first switch and the second switch opened. After the conversion is completed to the same voltage and the same phase as the voltage of one bank which is the output side, the first switch is closed, and then the primary cutout of one bank is opened, and then the other is turned on by the inverter circuit. The output voltage is gradually returned so as to have the same voltage and the same phase as the voltage of the input terminal side which is the bank side of the bank, and after returning the voltage, the second switch is closed and the other is connected via the bypass circuit. Power is supplied from the bank to the load side of one bank,
Switching is performed without interruption.

[0013] In the second invention, the low-voltage uninterruptible uninterruptible return method for a transformer is a method in which power is supplied from the other bank to the load of one of the banks via a bypass circuit. When switching back to the bank, shut off the bypass circuit and close the first switch to activate the inverter circuit first so that it has the same voltage and the same phase as the voltage of the input terminal side which is the other bank side, and then In the same inverter circuit, the output voltage is gradually returned to become the same voltage and the same phase as the voltage on the output side of one bank, and after the return to the voltage on the output terminal side of one bank is completed, Is closed without interruption by closing the primary cutout of the bank. In the transformer low-voltage uninterruptible switching device according to the third invention, switching of banks by uninterruptible power of the transformer by the method of the first invention and the second invention,
Failback is performed.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIGS. As shown in FIGS. 1 and 2, a primary cutout PC is connected to each of the phases U, V, and W of the distribution line L on the high voltage side of the transformers Tra and Trb provided in both the banks A and B. . Also, A,
A low-voltage uninterruptible switching device S is detachably connected between the low-voltage sides of both B banks via a bypass cable K.

The low-voltage uninterruptible switching device (hereinafter, referred to as a switching device) S will be described. The switching device S includes a first conversion circuit 1 and a second conversion circuit 2 which are two systems.

A rectifier section 3, a waveform correction section 4, an inverter circuit 5, a waveform correction section 6, an overcurrent limiting circuit 11, an AC switch section 7 as a first switch, and a control circuit 8 are provided for each of the conversion circuits 1 and 2. Have. Then, the first conversion circuit 1
In, the input terminal is connected to the PC1 terminal of the bank A (the power transformer side), and the output terminal is connected to the PC1 terminal of the bank B.

The second conversion circuit 2 has an input terminal A
It is connected to the C1-C2 terminal (shared transformer side) of the bank via the changeover switch 10, and the output terminal is connected to the C1-NC2 terminal of the B bank. The rectifier unit 3
Is composed of a single-phase bridge rectifier circuit and performs full-wave rectification on the input voltage from the A bank. The waveform corrector 4 corrects the waveform, and the inverter circuit 5 converts the voltage phase and voltage value. Further, the waveform corrector 6 further corrects the waveform of the power output from the inverter circuit 5.

The overcurrent limiting circuit 11 includes a current sensor such as a CT, and connects the A bank and the B bank in a loop.
During the parallel operation of the switching device S and the B-bank transformer until the primary cutout PC of the bank is opened, an excessive current flows from the inverter circuit 5 due to the voltage difference due to the difference between the voltage waveform of the switching device S and the voltage waveform of the B-bank. The overcurrent is detected and a detection signal is output to the control circuit 8 so as not to flow out. The AC switch unit 7 is made up of a triac or a thyristor, and is turned on / off by operation of various switches such as a bypass / inverter changeover switch 12a as switch control means provided on the operation panel 12 of the switching device S and a bypass circuit described later. Switching of the AC switch unit 9 as the second switch of B is possible.

The control circuit 8 as the first control means and the second control means includes a central processing unit (CPU), a voltage detection phase detection circuit, and an inverter control unit, and is connected between the input side and the output side of the system. Have been. The control circuit 8 has a readable / writable memory (hereinafter, referred to as RAM) 8a and a read-only memory (hereinafter, referred to as R) storing a control program and the like.
OM) 8b. Then, when the input and output terminals of the system are applied, the voltage detection phase detection circuit of the control circuit 8 outputs the voltage values applied to both terminals,
The phase and the phase rotation can be detected. Further, the inverter control section can control the inverter circuit 5.
Further, the inverter control section controls the inverter circuit 5 based on the detection signal from the overcurrent limiting circuit 11 to reduce the inverter output voltage.

The control circuit 8 is provided with a conversion switch for adjusting the input voltage waveform from the A bank of the operation panel 12 provided in the switching device S to the B bank voltage waveform, and converts the inverter output voltage waveform of the switching device S into the A bank. The inverter circuit 5 is controlled by operating a reverse conversion switch (both not shown) for adjusting to the input voltage waveform. With this control, the phase of the single-phase input voltage on the shared transformer side and the phase of the single-phase input voltage on the power transformer side can be independently varied in the range of -180 ° to + 180 °.

Further, the control circuit 8 controls the display of various messages on a display unit 13 provided on the operation panel 12. When the phase applied to the input / output terminal is reverse rotation based on the detection result of the phase rotation, the control circuit 8 controls the changeover switch 10 to connect the input terminals C1 and C2 of the second conversion circuit 2 to each other. The connection to the rectifier unit 3 is switched.

The bypass circuit B is connected between the input terminal and the output terminal of each system so that the switching operation of the AC switch unit 9 enables efficient operation of the switching device S when it is in operation. The AC switch unit 9 includes a triac or a thyristor. The AC switch unit 9 is provided in the switching device S and can be turned on / off and switched with the AC switch unit 7 by operating the operation panel 12.

The no-fuse breaker NFB is provided on the input and output terminals of the first conversion circuit 1 and the second conversion circuit 2, and is connected to the connection terminals P and C1 by an external operation from an operation panel provided in the switching device S. , C2 can be opened and closed, and is opened when the switching device S is internally short-circuited and when the bank B side is short-circuited or overloaded.

Now, a description will be given of a case where the load LB of the B bank is switched to the A bank while the switching device S is connected between the A and B banks via the bypass cable K as described above.

First, with the first conversion circuit 1, the second conversion circuit 2 and the AC switch sections 7 and 9 of the bypass circuit B in the switching device S open, the no-fuse breaker NFB is operated by an external operation from the operation panel. Is closed. In this state, the phase rotation of the input side and the output side is detected by the phase detection circuit of the control circuit 8, and if the phase rotation is the reverse rotation, the changeover switch 10 is controlled to control the input terminals C1 and C2. Swap the connection with. In this embodiment, the bank A has the connection shown in FIG. 4A, and the bank B has the connection shown in FIG. In this case, since the phase rotation is the reverse rotation, C1 and C2
(See FIG. 5B). Then, the output voltage of the inverter circuit 5 is converted to the same phase and the same voltage as the output terminal voltage. That is, as shown in FIG. 5B and FIG. 5C, the vectors between the respective phases are converted by 120 °. When this conversion is completed, the converted voltage value and phase are set to R
AM8a, and the control circuit 8 controls the operation panel 12
Of the conversion is displayed on the display unit 13.

After this display, the operator operates the operation panel 12 to turn on the AC switch section 7. Therefore, in this state, the load LB of the bank B is received from both the switching device S and the bank B.
Is supplied with power. Then, the primary cutout PC of the B bank is released. Thereafter, the switching device S
Supplies power to the load LB of the B bank. In this embodiment, as shown in FIG. 5C, the vector between VW and the vector between UV are different from those in FIG. 4C, but there is no problem in practical use.

Next, when the reverse conversion switch of the operation panel 12 is turned on, the inverter control section of the control circuit 8 gradually returns the output voltage of the inverter to the same phase and the same voltage value as the input terminal voltage. When the reverse conversion is completed, the control circuit 8 displays on the display unit 13 a display indicating the completion of the conversion. After confirming this display, the operator checks the operation panel for the bypass / inverter selector switch 12a.
To the bypass side. With this operation, the AC switch unit 7 is turned off, and the AC switch unit 9 is turned on. Accordingly, thereafter, power is supplied from the bypass circuit B of the switching device S to the load LB of the B bank.

In this state, the switching is completed, and after that, the construction of the bank B may be performed. Next, the cutback operation will be described. When the bypass / inverter changeover switch is set to the inverter side after the construction of the bank B is completed, the AC switch section 7 is turned on and the AC switch section 9 is turned off. Therefore, thereafter, B
Power is supplied to the load LB of the bank. Next, when the conversion switch is turned on, the control circuit 8 gradually converts the inverter output voltage into the voltage value and the phase stored in the RAM 8a. When the conversion is completed, the control circuit 8 displays the display unit 13.
Indicates that the conversion is completed.

Thereafter, the primary cutout PC of the B bank is inserted. Therefore, in this state, the switching device S
Power is supplied to the load LB of the bank B from both the bank and the bank B. Thereafter, the no-fuse breaker NFB is opened by an external operation from the operation panel 12, and the switching device S and the bypass cable K are removed from both banks.

In the above-described embodiment, the phase rotation on the input side and the output side is reverse rotation. For example, the connection of the transformer in bank A is shown in FIG. FIG.
In the case of (b), the rotation is the same. In such a case, as shown in FIG. 6, the control circuit 8 controls the vector between the phases to rotate the phase by 120 ° in the opposite direction to the above. .

In this embodiment, when the phase detection circuit of the control circuit 8 detects that the input side and output side phase rotations are reverse rotations, the control circuit 8 controls the changeover switch 10 to actuate. C1 and C1 on the input terminal side for the second conversion circuit 2
2 can be connected in reverse to each other.

In this embodiment, after the bank A and the bank B are connected in a loop, the switching device S and the bank B transformer are operated in parallel until the primary cutout PC of the bank B is opened. Even if a voltage difference occurs due to a difference between the voltage waveform and the voltage waveform of the bank B, the overcurrent limiting circuit 1
1 detects an overcurrent and the control circuit 8 lowers the inverter output voltage, so that an excessive current does not flow out of the inverter unit 5 and the inverter unit 5 can be prevented from being damaged.

Next, a second embodiment will be described with reference to FIG.
Note that the same components as those in the above embodiment and corresponding components are denoted by the same reference numerals, and description thereof is omitted. In this embodiment, the second conversion circuit 2 and the changeover switch 10 of the above embodiment are omitted, and the rectifier section 3 of the conversion circuit 1 is constituted by a three-phase bridge circuit instead, and the input terminal thereof is connected to the P terminal of the A bank.
-C1 terminal (power transformer side) and C1-C of A bank
2 terminals (shared transformer side), output terminals are PC1 terminal of B bank and C1-NC2 of B bank
The place connected to the terminal is different. The power detection phase detection circuit of the control circuit 8 detects the voltage values, phases, and phase rotations on the input side and the output side, and can control the inverter circuit 5 based on the detection results. That is,
The phases of the three-phase input voltages on the common transformer side and the power transformer side can be varied.

The operation of the second embodiment will be described. Now,
A case where the load LB of the B bank is switched to the A bank in a state where the switching device S is connected to both the A and B banks via the bypass cable K as described above will be described.

First, the no-fuse breaker NFB is closed by an external operation from the operation panel 12 with the AC switches 7 and 9 of the conversion circuit 1 and the bypass circuit B in the switching device S open. In this state, the phase rotation of the input side and the output side is detected by the phase detection circuit of the control circuit 8, and if the phase rotation is the normal rotation, the phase rotation is reversed by connecting the input terminals C1 and C2 as they are. If it is a rotation, the output voltage of the inverter circuit 5 is converted into the same phase and the same voltage as the output terminal voltage by reversely connecting the input terminals C1 and C2 in the same manner. When this conversion is completed, the voltage value and the phase after the conversion are stored in the RAM 8a, and the control circuit 8 operates the display unit 1 of the operation panel 12.
At 3, the completion of conversion is displayed.

After this display, the operator operates the operation panel 12 to turn on the AC switch section 7. Therefore, in this state, the load LB of the bank B is received from both the switching device S and the bank B.
Is supplied with power. Then, the primary cutout PC of the B bank is released. Thereafter, the switching device S
Supplies power to the load LB of the B bank.

Next, when the reverse conversion switch of the operation panel is turned on, the inverter control section of the control circuit 8 gradually returns the output voltage of the inverter to the same phase and the same voltage value as the input terminal voltage. When the reverse conversion is completed, the control circuit 8 displays on the display unit 13 a display indicating the completion of the conversion. After checking this display, the worker
The bypass / inverter selector switch 12a of the operation panel is set to the bypass side. With this operation, the AC switch unit 7 is turned off, and the AC switch unit 9 is turned on. Therefore,
Thereafter, power is supplied from the bypass circuit B of the switching device S to the load LB of the B bank.

In this state, the switching is completed, and after that, the construction of the bank B may be performed. Next, the cutback operation will be described. After the construction of Bank B is completed, if the bypass / inverter changeover switch 12a is set to the inverter side,
The AC switch 7 is turned on, and the AC switch 9 is turned off. Accordingly, thereafter, power is supplied from the inverter side of the switching device S to the load LB of the B bank. Next, when the conversion switch is turned on, the control circuit 8 gradually converts the inverter output voltage into the voltage value and the phase stored in the RAM 8a. When the conversion is completed, the control circuit 8 displays on the display unit 13 that the conversion is completed.

Thereafter, the primary cutout PC of the B bank is inserted. Therefore, in this state, the switching device S
Power is supplied to the load LB of the bank B from both the bank and the bank B. Thereafter, the no-fuse breaker NFB is opened by an external operation from the operation panel 12, and the switching device S and the bypass cable K are removed from both banks.

In this embodiment, when the phase detection circuit of the control circuit 8 detects that the input and output phase rotations are reverse rotation, the control circuit 8 automatically controls the input terminal side. The same effect as when C1 and C2 are connected in reverse is obtained.

The present invention is not limited to the above embodiment. For example, in the first embodiment, the phase rotation on the input side and the output side in the phase detection circuit of the control circuit 8 are reverse rotations. When the control circuit 8 detects that
Although the input terminals C1 and C2 are automatically connected to each other in the reverse order, the connection can be manually made instead, and can be arbitrarily changed without departing from the spirit of the present invention.

[0042]

As described above, according to the present invention, bank switching / returning can be performed without a complete power failure, and only one switching device is required. The difference between the voltage taps of the transformers can be absorbed by the switching device, so that there is an excellent effect that the switching connection between the banks having two different ground phases of the transformers of both banks is not disabled. .

[Brief description of the drawings]

FIG. 1 shows a first embodiment of the present invention, and is a conceptual circuit diagram in which a switching device is connected to a low voltage side between both banks.

FIG. 2 is an electric circuit diagram of the switching device.

FIG. 3 is an electric circuit diagram of the operation panel.

FIGS. 4A, 4B, and 4C are explanatory diagrams showing various connections of transformers by vectors.

FIG. 5 is an explanatory diagram in the case of converting the connection (a) of the converter to (c).

FIG. 6 is an explanatory diagram in the case of converting the connection (a) of the converter to (b).

FIG. 7 is an electric circuit diagram of a switching device according to a second embodiment of the present invention;

FIG. 8 is a circuit diagram showing a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... 1st conversion circuit, 2 ... 2nd conversion circuit, 3 ... Rectifier part, 4 ... Waveform correction part 5 ... Inverter circuit, 6 ... Waveform correction part, 7 ... AC switch part as a 1st switch, 8 ... Control circuit as first control means and second control means, 9 ... AC switch section as second switch, 10 ... changeover switch, 12a
... Bypass / inverter selector switch as switch control means, Tra, Trb ... Transformer, L ... Distribution line, PC
… Primary cutout, K… Bypass cable,
B: bypass circuit, S: switching device, NFB: no fuse breaker.

Claims (3)

(57) [Claims] A switching device including an inverter circuit having a first switch and a bypass circuit connected in parallel to the inverter circuit and having a second switch is provided between one bank and the other bank. When switching between one bank and the other bank, with the first switch and the second switch open, the inverter circuit first makes the output voltage the same as the voltage on one bank side which is the output side. After the conversion to the voltage and the same phase is completed, the first switch is closed, and then the primary cutout of one bank is opened. The output voltage is gradually returned so as to have the same phase, and after returning the voltage, the second switch is closed, the first switch is opened, and the other switch is opened via the bypass circuit. Low uninterruptible switching method of a transformer and supplying power to the load side of one of the banks from the bank. 2. A switching device comprising an inverter circuit having a first switch and a bypass circuit connected in parallel to the inverter circuit and having a second switch is provided between one bank and the other bank. In the state where power is supplied from the other bank to the load of one bank via the bypass circuit, when switching back from the other bank to one bank, the second switch is turned off and the bypass is turned off. The circuit is cut off and the first switch is closed to operate the inverter circuit first so that the same voltage and the same phase as the voltage of the input terminal side which is the other bank side, and then one of the inverter circuits is operated by the same inverter circuit. After gradually returning the output voltage to the same voltage and the same phase as the voltage of the output terminal side which is the bank side, after the return to the output terminal side voltage of one bank is completed, Low pressure uninterruptible switchback method of the transformer, characterized in that closing the primary cut-out of the square of the bank. 3. An inverter circuit comprising a first switch.
When, a bypass circuit having a second switch which is connected in parallel with its inverter circuit, said inverter circuit such that the output voltage on the output side bank side of the voltage and the same voltage and the same phase After performing the conversion control, the output voltage becomes the same voltage and the same phase as the voltage of the bank which is the output side, and then the output voltage is changed so that the output voltage becomes the same voltage and the same phase as the voltage of the original input terminal side. First control means for controlling the inverter circuit so as to gradually return the output voltage, and conversion control of the inverter circuit so that the output voltage becomes the same voltage and the same phase as the voltage on the bank side which is the input side. After the output voltage becomes the same voltage and the same phase as the voltage of the bank on the input side, gradually return the output voltage to the same voltage and the same phase as the voltage of the bank on the output side. A second control means for controlling said inverter circuit, the first scan as follows during the return bank changeover and bank switching
Switch control means for controlling the switch and the second switch;
Transformer low-voltage uninterruptible switching device equipped with. (When switching banks) (1) When switching between one bank and the other bank,
Leave the first switch and the second switch open.
You. (2) In the inverter circuit controlled by the first control means
And the output voltage is compared with the voltage of one bank which is the output side.
Close the first switch after conversion to the same voltage and phase
Control. (3) After that, the primary cut-out of one bank
After releasing the point, the point controlled by the first control means is released.
The inverter circuit has the same voltage as the input voltage of the other bank.
After returning the output voltage to
The switch is controlled to close, and after the second switch is closed, the first
Switch is opened. (At the time of bank switching back) (1) One bank from the other bank via a bypass circuit
While power is being supplied to the bank load, the other bank
When switching back from the bank to one bank, close the first switch.
After opening the first switch, open the second switch
A first switch with blocking the bypass circuits and
Close.