IEEE C37.93-1987 pdf free.IEEE Guide for Power System ProtectiveRelay Applications of Audio Tones overTelephone Channels.
IEEE C37.93 Solid state audio-tone equipment operates at voltages typically below 24 V direct current. This is not usually theconcern of the power application engineer because of the integral power supplies that go with these equipments.Practically all such power supply units are designed with regulators to maintain output voltage to assure performance of the tone equipment within its specified limits. These supplies operate from standard power station sources: 120 valternating current,24,48,125, and 250 V direct current (ANSIIEEE Std 281-1984)[3J.2 In applying solid stateequipment,care should be taken to insure that the power supply ratings are adequate for battery equalizingovervoltages.
Power supplies in newer type audio-tone equipment are of the DC-DC converter type. The isolation afforded by thistype of supply reduces the effects of surges appearing at the power supply input, and is of particular benefit when thestation battery is used as the source. Converter type power supplies are preferred over the less effective droppingresistor and tapped station battery techniques.
From an operating point of view, the use of the station battery may be preferable to a separate battery since it reducesmaintenance.
For solid state equipment, there are advantages to separate battery sources since this equipment usually operates below48 V. This method of supply has the advantage of being independent of the station battery source, thus minimizingexposure to surge phenomena originating in the station battery circuits.
Alternating current as a source of power is suitable only when supplied from an uninterruptible power source (UPS).3.3.5 Telephone Company Power Requirements
Particular attention should be given to the power requirements for any on-site active network channel terminatingequipment owned by the telephone company. If this equipment is essential to the proper operation of relay schemes,the same considerations listed in this section must apply.IEEE C37.93 pdf download.