TABLE OF CONTENTS All but the smallest substations include auxiliary power supplies. AC power is required for substation building small power, lighting, heating and ventilation, some communications equipment, switchgear operating mechanisms, anti-condensation heaters and motors. DC power is used to feed essential services such as circuit breaker trip coils and associated relays, supervisory control and data acquisition (SCADA) and communications equipment. This chapter describes how these auxiliary supplies are derived and explains how to specify such equipment.
Capital cost and reliability objectives must first be considered before defining the battery and battery charger combination to be used for a specific installation. The comparison given in Table 4.1 describes the advantages and disadvantages of three such combinations.
| Type | Advantages | Disadvantages |
|---|---|---|
| 1. Single 100% battery and 100% charger | Low capital cost | No standby DC System outage for maintenance Need to isolate battery/charger combination from load under boost charge conditions [1] in order to prevent high boost voltages appearing on DC distribution system [2] |
| 2. Semi-duplicate 2 50% batteries and 2 100% chargers | Medium capital cost Standby DC provided which is 100% capacity on loss of one charger Each battery or charger can be maintained in turn. Each battery can be isolated and... |
