CONTROL POWER SUPPLIED TO THE RELAY MUST BE CONNECTED TO THE MATCHING POWER SUPPLY
RANGE OF THE RELAY. IF THE VOLTAGE IS APPLIED TO THE WRONG TERMINALS, DAMAGE MAY
The L90 relay, like almost all electronic relays, contains electrolytic capacitors. These capacitors are well
known to be subject to deterioration over time if voltage is not applied periodically. Deterioration can be
avoided by powering the relays up once a year.
The power supply module can be ordered for two possible voltage ranges. Each range has a dedicated input connection for
proper operation. The ranges are as shown below (see the Technical Specifications section for additional details):
LO range: 24 to 48 V (DC only) nominal
HI range: 125 to 250 V nominal
The power supply module provides power to the relay and supplies power for dry contact input connections.
The power supply module provides 48 V DC power for dry contact input connections and a critical failure relay (see the
Typical Wiring Diagram earlier). The critical failure relay is a Form-C that will be energized once control power is applied
and the relay has successfully booted up with no critical self-test failures. If on-going self-test diagnostic checks detect a
critical failure (see the Self-Test Errors table in Chapter 7) or control power is lost, the relay will de-energize.
A CT/VT module may have voltage inputs on Channels 1 through 4 inclusive, or Channels 5 through 8 inclusive. Channels
1 and 5 are intended for connection to Phase A, and are labeled as such in the relay. Channels 2 and 6 are intended for
connection to Phase B, and are labeled as such in the relay. Channels 3 and 7 are intended for connection to Phase C and
are labeled as such in the relay. Channels 4 and 8 are intended for connection to a single phase source. If voltage, this
channel is labelled the auxiliary voltage (VX). If current, this channel is intended for connection to a CT between a system
neutral and ground, and is labelled the ground current (IG).
a) CT INPUTS
VERIFY THAT THE CONNECTION MADE TO THE RELAY NOMINAL CURRENT OF 1 A OR 5 A MATCHES
THE SECONDARY RATING OF THE CONNECTED CTs. UNMATCHED CTs MAY RESULT IN EQUIPMENT
DAMAGE OR INADEQUATE PROTECTION.
Figure 3–9: CONTROL POWER CONNECTION
L90 Line Differential Relay
3.2.3 CONTROL POWER
3.2.4 CT/VT MODULES