Advertisement
GEK-26423
The normally closed contacts between terminals 19 and 20 will close, carry continuously, or interrupt
0.3 amperes in non-inductive circuits up to 250V DC.
OPERATING PRINCIPLES
The inho type
units
in the C[YG51A relay are of the four—pole induction-cylinder construction (see
Fig. 6) with schematic connections as shown
in
Fig. 3.
The two side poles, which are energized by the
phase-to-phase vol tage in quadrature with
the
phase- to—neutral vol tage of the protected phase, produce the
polarizing flux.
The flux in the front pole, which is energized by a percentage of the phase-to-neutral
vultaçje of Lire protected phase, interacts with the polarizinq flux to produce restraint torque.
The flux
in the rear pole, which is energized by the line current of the protected phase, interacts with the polar
i z
i
rig
flux to produce operating torque.
The torque at the balance point for the phase A starting unit can, therefore, be expressed by the
following equation:
Torque
=
0
=
KI'aEbc cos
((
-30)
—
TE'aEbC' sin 8
(1)
where:
K
design constant
=
Phase-A-to-neutral voltage at the relay location
Ebc
=
Phase B to Phase C voltage (Eb
-
E) at the relay
=
Phase A current, at the relay location
B
=
Angle by which Ea leads Ebc' (900 for balanced 3-phase condition)
T
=
Restraint tap setting
=
Angle by which
'a'
leads Eb
CHARACTERISTICS
The operating characteristics of the mho units in the CEYG51A relay may be represented on the R-X
impedance diagram as shown in Fig. 7.
It should be noted that these steady-state characteristics are for
rather specific fault conditions described below:
The mho unit has a circular characteristic which passes through the origin of the R-X diagram.
The
diameter passing through the origin defines the angle of maximum torque of the unit, which occurs when
line current (a for example) leads the quadrature polarizing voltage (Ebc for example) by 30°.
Since
there is essentially no phase shift in the line—to-neutral voltage for a single-phase-to-ground fault,
this maximum torque angle (i.e. maximum reach angle) occurs when the line current lags the phase—to—neutral
voltage by 600, which is the condition represented in Fig. 8.
The diameter of the impedance circle would nonially be considered as the ohmic reach of the unit,
which would be the basic minimum reach with the F
tap leads on 100 percent.
However, if the mho unit is
not compensated it is not an accurate distance measuring until except on 3—phase faults, or for the
special case
of
single-phase—to-ground faults where the zero-sequence impedance to the fault is equal to
the positive sequence impedance to the fault.
Instructions are given in Appendices II and III for
selecting a reach setting.
The ohmic redch of the inho unit can be extended by reducing the percentage of the faut voltage
applied to the restraint circuit, that is by setting the E 2 tap leads on
a
lower percentaoe position on
the tap block.
(Zi)
100
Ohmic Reuch
=
2
E
Tap Setting
()
(5)
5
Advertisement
