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SYNCHRONISM
CHECK EQUIPMENT
Introduction

It is used to check whether or not two parts of
the same system or two separate systems are in
synchronism with each other.
 Synchronism check devices are basically
permissive devices
 Synchronism check devices do not initiate
reclosing.
 These devices require single-phase (line-to-line
or line-to-neutral) potentials from the same
phase(s)
Classification
 There
are two kinds of synchronism check
equipment available.
 1--->>IJS
# Slow-speed device
 2--->>GXS
# High-speed device
Operating principle of IJS

The ijs relay is an induction disk device that receives single-phase voltages
from the same phase(s) on both sides of the circuit breaker.

Two electromagnets each has two coils.

In the first operating electromagnet

Coils are connected in such a way that they receive the vector sum of
voltages (incoming Vi and running Vr).
Top=kop(Vi -Vr) 2 ---------------------(1 )
two
kop is a design constant.
The second electromagnet is the restraining device.
It receives the vector difference of the incoming & running voltages from
the same phase(s)
.
Tr=kr(Vi+Vr) 2 ---------------------(2)
kr is a design constant.
contd.



IN addition to electrical torques in the relay, there is also a
mechanical restraint in the form of the control spring.
So net torque operating in the relay is
T = kop (Vi+Vr) 2 - kr (Vi -Vr) 2 - k s
since ks is small as compare to electrical torques, so the
2
2
above eqn. becomes T= kop (Vi+Vr) - kr (Vi -Vr)
-------------------->>(3)
# It should be noted that with equal voltages on the running &
incoming busses, (Vi + Vr) will be equal to (Vi - Vr) when Vi & Vr
are 90 degrees apart.
# As the two voltages approach each other in phase angle,
(Vi+Vr) will become greater than (Vi - Vr) & vice versa.
# Thus the net operating torque tends to increase as the two
systems tends to be more in phase with each other.
# Whether net torque is in the operating direction (T>0) or in the
restraining direction (T<0) will also depend on the relative
magnitudes of k op & kr

In all ijs relays kr is designed to be greater than
kop
# So the net torque goes from restraining to
operating at some angular separation that is
smaller than 90 degrees.
# This angle is called the closing angle.
# Some ijs relays have fixed closing angle while
others have closing angles that are adjustable.
 The operating time of the ijs is determined by
two factors ,

1Strength & position of the permanent
drag magnet that the acts on the disk to slow
its motion.
2- Rotary distance that the disk has to
travel to close the contacts.
//- Since kr > kop, if only one voltage is applied to the
relay the T will be –ve &the relay contacts will be held
open.
//-This is apparent from eqn.3
//-With neither voltage applied, the net electrical T is
Zero, but the spring will keep the contacts of the relay
open.
//-Thus , in order for the ijs relay to close its contacts,
there must be voltage present on both sides of the
circuit breaker, & the phase angle between these
voltages must be within the closing angle setting the
relay.
//-This means that the synchronism check unit by itself
will not permit picking up a dead line.
-----Some models of the ijs include these dead
line & dead bus aux. (Vi + Vr) iliry devices , while
others do not.
OPERATING CHARACTERISTIC
OF IJS
Internal connections for IJS

There are several
different model of ijs
relays.
 IJS51A
FEATURES & BENEFITS OF IJS
 Telephone
type relay units available.
 Mechanical targets available.
APPLICATION OF IJS RELAYS
 These
relays find application wherever
slow-speed synchronism check for
automatic or manual closing of a line
terminal is required.
 Synchronism time delay.
 Instantaneous bus & line undervoltage.
OPERATING PRINCIPLES
OF GXS //
 High
speed device with a lock out feature.
 This relay is comprised of three units.
1- time delay (T) induction disk unit
similar to that in the ijs relay
2- instantaneous (i) induction cup voltage
unit. Provides the closing angle.
3- a dc-operated auxiliary lockout unit (x)
for indicating to the circuit breaker.
contd.
 Torque
equn. is same as ijs relay
T=kop(Vi +Vr)2-kr(Vi-Vr)2
 The only diff. is in kop & kr
 These constants are such that the closing
angle of the disk unit is appx. 85 degrees.
 Other diff. apparent from equn., is the
strength of the drag magnet.
# In GXS, the drag magnet is weak so that
the unit operates quit a bit faster than the
IJS.
Instantaneous cup unit
# like the disk unit
# connected to receive both
running (bus) & incoming (line)
voltages.
#Electrical torque developed
Te=k vivr sin Ø
where k =design constant
vi=magnitude of incoming voltage
vr=magnitude running voltage
Ø =angle by which vr leads vi

Suppose for a condition where vr leads vr
by say 30 degrees , then Te=0.5 k vivr
If vi leads vr by same degrees then,
Te= - 0.5 k vivr
Thus Te at rated voltage proportional to
the sine of the angular separation of the two
voltages, but the direction of the torque will
depend on which voltage is leading.
The contact assembly as shown in the next slide
The cup shaft is fastened to the lever arm plate
so that they rotate together.
A spring with adjustable tension






A spring with adjustable tension is provided so
that Te is equal to mechanical torque of the
spring (ks)
Now equn.4 becomes
ks = k vi vr sin Ø --------->>(5)
This equn. Shows that the calibration of the
instantaneous cup unit is dependent on the
applied voltages.
The GXS12A relay also includes a dc-operated
auxiliary unit. This has a time delay pick-up of
about six cycles, & it is incorporated in the relay
to provide a lockout feature.
This relays depend upon the fixed closing angle
at which the relay is set & the cut-off-frequency
diff. of the voltages applied to the relay.

The max. slip for which the relay will permit closing may
be approximated from the curves34 by taking the
following steps: 1>read the operating time of the disk
unit from the curve of phase angle diff. that is same as
the closing angle

2>repeat 1 above for the zero phase angle curve.

3>calculate the avg. time from the results of 1 & 2
above.

4>divide twice the closing angle setting of the cup
unit by 360 times the time calculated in 3 above.
The result is max. slip cycles per second for which the
relay could permit closing.
 Another important cha. Is that from fig.21 ,
The magnitudes of the applied voltages have a significant
effect on the actual closing angle, & that the higher the
closing angle setting, the greater is this effect.
FETURES OF GXS
 10
to 45 degree closing angle adjustment.
 10 to 99 cycles time delay adjustment.
APPLICATION OF GXS
 Used
in high-speed automatic reclosing on
transmission lines.
 Hydraulic turbine-driven generators.
 Internal combustion driven generators.
 Tie line or bus-tie circuits.
CONCLUSION
 It
is reliable & efficient.
 It is applicable to other fields such as
hydraulics etc..
 Cost is less & maintenance is also less.
 And always useful in power system.
…..
REFERENCES
 www.GEindustrial.com/Multilin
 www.GEindustrial.com/pm