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TARGET SEAL-IN UNIT
The target seal-in unit connected to studs 1 and 11 in the SPA 11 B and SPA 12B relays
has the ratings and characteristics shown in Table Ill.
RATINGS AND CHARACTERISTICS OF THE TARGET SEAL-IN UNIT
DC Resistance
Minimum Operatin g (Amperes)
Carry Continuously (Amperes)
Carry 30 Amps for (Seconds)
Carry 10 Amps for (Seconds)
60 Hz Impedance (Ohms)
Minimum Dropout (Amperes)
SEISMIC CAPABILITY
The Seismic Fragility Level exceeds 3.5g ZPA when tested using a biaxial multi
frequency input motion to produce a Required Response Spectrum in accordance with
ANSI/IEEE C37 .98-1978, Standard for Seismic Testing of Relays.
OPERATING PRINCIPLES
The Type SPA relays are designed to detect an open pilot-wire, a shorted pilot wire,
and a grounded pilot wire in a protective system using pilot-wire relays. Type SPD pilot
wire relays are covered by instruction book GEK-49794.
The Type SPA relays operate by circulating a small direct current of approximately
0.75 milliamperes through the pilot wire. The current is provided by the power supply of
the sending-end monitoring relay (SPA 11A or SPA 11B). The receiving-end monitoring
relay(s) (SPA 12A or SPA 12B) completes the circuit loop for the circulating current without
adding or subtracting (sourcing or sinking) any current.
OPEN PILOT WIRES
The undercurrent units in the SPA relays are energized (or picked up} under normal
operating conditiops. When an open circuit of the pilot wire occurs, the current drops to
zero and the undercurrent units in both receiving- and sending-end relays drop out and
the UC LED indicators light. This is the extreme case of the undercurrent condition. The
undercurrent units will drop out for the circulating currents indicated below.
GEK-65512
TABLE Ill
10% (Ohms)
+
CHARACTERISTICS
0.2
7
0.2
0.3
0.03
0.25
52
0.05
6
TAP
2.0
0.13
2.0
3
4
30
0. 53
0. 5
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