Fault Driven Power Supplies

A source of auxiliary power is generally required in circuit breaker applications in order to provide power to close and trip coils and to allow protective relays to operate reliably.

 

In certain applications it may be uneconomic or contrary to safety regulations to use a DC battery to provide auxiliary power (e.g underground coal mines). It is not recommended to derive auxiliary power directly from the local AC voltage alone. Under fault conditions this voltage may instantaneously fall to such a level that circuit breaker shunt trip coils or protection relays may not operate correctly.

 

NEPEAN Power's Fault Driven Power Supply is designed to overcome these problems. Under normal load conditions it uses the local 110VAC to charge storage capacitors to form a DC bus. Under fault conditions the local voltage may fall, but this generally leads to an increase in current flow. This current is used as an energy source to supplement the available internal bus voltage maintained on the capacitors. The Fault Driven Power Supply is available in two versions to suit 1A or 5A CT secondaries as required.

 

The output of the Fault Driven Power Supply is 48VDC and is used to trip circuit breakers and/or power other protective devices. Primary input power to the Fault Driven Power Supply is 110VAC with a secondary power input of 3 circuits from current transformers on the mains input to the equipment being protected. The unit provides a regulated 48V supply capable of continuous 500mA with a short term pulse capability of 10A. This allows the Fault Driven Supply to be used to power both protection relays and also heavily rated shunt trip circuits on main circuit breakers.

 

Three additional outputs are provided which may be used for monitoring or included as additional protection in control circuits. These contacts are; 1) Mains Healthy, which closes when there is 110VAC present, 2) 48V Healthy which is operated when there is greater than 45V on the output terminals and 3) Shunt Trip Voltage Output, which may be used as a pseudo no-volt circuit, this output turns on when the bus volts drop from a healthy state (of greater than 45V) to 36V. This directly connects the DC bus to the shunt trip terminal and is intended to directly operate the shunt trip of a breaker. This would only be used if it is intended that the main breaker is to be opened upon loss of input supply.

 

The Fault Driven power supply is also current limited to protect against overloading. Over loading may easily occur if a shunt trip coil is left in circuit on power up, which may be the case in the event of an emergency stop button being operated and not released. If operating in current limit a red LED on the front panel will be on. If the current limit condition continues the unit will switch off to protect the power supply from overheating and causing permanent internal damage. This second condition is indicated on the front panel with an Over Temperature LED.

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