OPTI-UPS DS160KD33 - Manual (Page 15)

1-11
The static switch is composed of two pairs of back-to-back connected SCR. It can
transfer the load from reserve to inverter or from inverter to reserve without dead
time at the output. Therefore, it is a very important portion of a UPS.
Detection circuitry is added to the control circuit to achieve zero dead time transfer.
Extra detection logic is employ to control when should the static switch transfer. For
example, when output is short circuited under normal mode operation, the UPS
detect the short circuit and stop the inverter after a period which the inverter can
endure, then the static switch will not transfer to reserve to prevent tripping and
hurting the reserve breaker. But in case of overload, the UPS will stop the inverter
after a period the inverter can endue, and then transfer the load to reserve because the
overload capability of the static switch is higher than the inverter.
Also the transfer action is determined according to the reserve-input voltage and
frequency to protect the load from supplying incorrect power to the load. At last,
there is a double check by the CPU whether the transfer is successful or not.
1.6. Maintenance Bypass Switch
Unlike other UPS, the maintenance bypass switch is already installed inside the UPS
for convenience. It should be opened under normal operation, and only closed during
maintenance. For the sake of maintenance personnel’s safety, all power supply inside
the UPS should be disconnected before touch any parts inside the UPS; therefore, the
maintenance bypass switch is a necessity to maintain AC power at the output and can
keep safe at the same time. If the bypass breaker is closed under normal operation,
the inverter will stop and the load will be automatically transferred to reserve to
prevent the inverter connect directly to the AC source. Of course, you cannot switch
on the inverter as long as the maintenance bypass breaker is closed.
The operation of the maintenance bypass breaker is that, switch off the inverter first
then the static switch will automatically transfer the load to reserve without dead
time. Then now you can close the maintenance bypass breaker now, and then open
the reserve breaker, so that the load can get AC from the output without interruption.