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Instructions manual (48 pages)

Table Of Contents

Table of Contents

receiving-end relays in the open position. An open pilot wire will result in the closure of

the UC contacts and operation of the UC LED at both the sending and receiving ends. A

shorted pilot wire, resulting in a significant increase in the monitoring current, will result

in closure of the contacts of the overcurrent (OC) function and operation of the OC LED in

the sending-end relay, and the closure of the UC function contacts at the receiving end. A

Specific information on the magnitude of the circulating current, and operating

levels of the UC, OC and ground-detection functions, is provided in the section on

CHARACTERISTICS.

tions of the SPA 11A and SPA 12A relays are provided in Figures 20 and 21 respectively.

When direct transfer tripping over the pilot wire is desired, in addition to the

monitoring functions, the SPA 11 B is required at the sending end and the SPA 128 at the

receiving end. These "B" relays include the necessary circuits to transmit and receive the

direct transfer-trip signals, as well as the functions required to monitor the pilot-wire

circuit as previously described. Typical elementary diagrams for a pilot-wire relaying

system with monitoring and transferred tripping are provided in Figure 22 for two

terminal lines and in Figure 23 for three-terminal line applications. These diagrams

illustrate the two-way transfer-trip application in which the transfer-trip signal is initiated

by either the sending- end relay (SPA 11 B) or the receiving-end relay {SPA 128). When the

transfer-trip signal is to be sent in one direction only, the same relays are applied but the

TT unit would not be used at the transfer-trip initiating end and the TTA unit would not be

used at the transfer-trip receiving end. Diagrams for the one-way transfer-trip application

are available upon request.

There are four types of SPA relays: 1) a sending-end relay, 2) a sending-end relay

with transfer-trip capability, 3) a receiving-end relay, and 4) a receiving-end relay with

transfer-trip capability. A sending-end relay with the transfer-trip feature may be used

with a receiving-end relay without the transfer-trip feature and vice versa. The basic

functions of the four types of SPA relays are outlined in the table below.

SENDING

RELAY

END

SPA 11A

SPA 11 B

SPA12A

SPA12B

Elementary diagrams for the two-terminal and three-terminal applica