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GEK-26437
MHO DISTANCE RELAY
TYPE
GCY5IF
DESCRIPTION
The GCY51F is a single—phase inho relay consistin g of two units and associate d auxiliari es mounted in the
large (La) double-ended case.
The lower unit is an M 1 unit which is designed for first zone applicati on.
The upper unit is an M 2 unit
which is designed for second zone applicati ons only.
The second zone is offset in the forward direction to
provide a
figure 8" characte ristic suitable for ling, heavily loaded lines.
GEK-26437 covers a 5 ampere,
60 hertz model (Form 1A) and a 1 ampere, 50 hertz model (Form 2A).
The impedance ranges and offsets are
shown in Table I.
Since the one ampere relay has five times the impedance range of the five ampere relay,
the applicati on and calculati on of setting discussio n is applicab le to the one ampere relay by multiply ing
the impedances by five.
The internal connecti ons diagram is as shown in Figure 13.
APPLICATION
The GCY51F relay is used for phase fault protectio n of a transmis sion line.
It has a distincti ve
figure eight' characte ristic which is obtained by using two separate mho units per phase of the line.
The
first zone mho unit, M
1
, has a characte ristic which passes through the origin of the R-X diagram as in the
usual applicati on.
The characte ristic of the second zone mho unit, M
2
,
s offset in the forward direction by
an adjustab le amount which allows overlapp ing of the two characte ristics.
See the R-X plot o the characte r
istics in Fig. 11.
The 'figure eight' characte ristic is applied where a relay with a long forward reach setting is required
and at the same time it is necessar y to accoirmiodate heavy line loadings or nhinor system swings without caus
ing relay operatio n.
The M 1 first zone unit may be used alone to provide instantan eous tripping for a portion of the protected
line.
The N 2 second zone unit is used with a timer to provide time-del ay back-up tripping for the balance of
the protected line and a portion of the next line section.
The trip contacts of both units connected in
parallel will provide the overreac hing tripping characte ristic needed for direction al comparison or trans
ferred tripping pilot—re laying schemes.
Typical external connecti ons are shown in Figs. l6A and B for the
scheme of protectio n describe d.
This shows the need for auxiliari es such as a timer and a tripping rectifier
for circuit isolation in addition to the auxiliari es needed for whatever type of pilot-rel aying scheme is
selected.
If the GCYS1F is used in a pilot-rel aying scheme with the line side potentia l and high speed reclosing ,
it is recorrieended that overcurr ent fault detectors be used to supervis e the trip circuits.
When setting the relay units, it is reconnended that the offset setting on the M 2 unit not exceed 80 per
cent of tho forward reach setting of the Ml unit.
This will insure at least a 20 percent overlap of the two
characte ristics based on the reach setting of the N 1 unit.
When selecting a basic minimum ohmic reach tap to
protect a line, it is desirable to select the highest one that will accoriiriodate the desired setting.
For
example, if a 5 ohm setting is desired on the M 1 unit, the tap selected should be 3 ohms minimum rather than
the 0.75 or 1.5 ohm tap.
This will insure the highest possible torque level in the relay.
Refer to the sec
tion on CALCULATION OF SETTINGS for a worked example of determin ing the required settings for a typical
applicati on.
Refer to the section on CHARACTERISTICS for the relay unit operatin g
time
curves, Fig. 8 and
Fig. 10 and the relay reach vs. fault current curves in Fig. 7 and Fig. 9.
In the normal transmis sion line applicati on the N 1 first zone unit reverse offset is set at zero.
Thus,
this unit will operate for faults only in the protected line section and not operate for bus faults behind
the relay location .
However, when the protected line ends in a transform er and the relay is connected to CT's
and PT's on the line side of the transform er, the M 1 first zone reverse of,set may be set at 0.5 ohm so as to
reach backwards part way into the impedance of the transform er bank.
Thus, the relay will remain picked up
even for a zero voltage line fault right at the transform er terminal s independent of first zone memory action.
The;e instructi ons do not purport to cover all details or variation s in equipment nor to provide for
ever.; possbie contingency to be met in connectIon with installati on,
operatio n or maintenance.
Should
further informat ion be desired or should particula r problems arise which are not covered sufficicn tly for
the purchase r's purposes , the matter should be reterz-ed to the General Electric Company.
To the extent required the products describe d herein meet applicab le ANSI,
IEEE and NEMA standard s;
but no such assuranc e is given with respect to local codes and ordinances because they vary greatly.
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