GE STD15C User manual

INSTRUCTIONS 37
WITH
GEK
-
45307
TRANSFORMER
DIFFERENTIAL
RELAYS
PERCENTAGE
AND
HARMONIC
RESTRAINT
TYPES
STD
15
C
AND
STD
16
C
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PHILADELPHIA
.
PA
.
POWER
SYSTEMS
MANAGEMENT
DEPARTMENT
ELECTRIC
GENERAL
Courtesy of NationalSwitchgear.com

GEK-45307
CONTENTS
PAGE
..
....................................................
DESCRIPTION .....................................................
APPLICATION .....................................................
CALCULATION OF SETTINGS .........................................
METHOD ....................................................
CURRENT TRANSFORMER CONNECTIONS ...........................
DETERMINATION OF CT TURNS AND TYPE RELAY TAP SETTING . .
CURRENT TRANSFORMER RATIO ERROR ...........................
PERCENT SLOPE SETTING....................?
..............
I DETERMINATION OF CT TURNS AND RELAY TAP SETTING
.....
11 PERCENT RATIO ERROR ....................................
IA REPEAT-CT TURNS AND RELAY TAP SETTING ..................
IIA REPEAT PERCENT RATIO ERROR ..........................
III PERCENT SLOPE SETTING .................................
RATINGS
.........................................................
AND ..............................
AUXILIARY RELAY CONTROL CIRCUIT ...........................
CHARACTERISTICS ..................................................
PICKUP AND OPERATING TIME .................................
OVERCURRENT UNIT PICKUP ...................................
PERCE N T AGE CHARACTERISTICS
...................
HARMONIC RESTRAINT CHARACTERISTICS ........................
BURDENS .........................................................
CONSTRUCTION. ...................................................
CURRENT TRANSFORMERS ............................................
THROUGH CURRENT RESTRAINT CIRCUIT .........................
DIFFERENTIAL CURRENT CIRCUIT ............................
OVERCURRENT UNIT ..........................................
OPERATING UNIT
.......................................
TARGET AND SEAL-IN UNIT ...................................
CASE
............................................................
RECEIVING, HANDLING, AND STORAGE ................................
ACCEPTANCE TESTS ................................................
VISUAL INSPECTION .........................................
MECHANICAL INSPECTION .....................................
ELECTRICAL TESTS ..........................................
TEST FACILITIES ...........................................
INSTALLATION PROCEDURE...................~ .....................
TESTS .....................................................
PICKUP ....................................................
HARMONIC CURRENT RESTRAINT ................................
THROUGH CURRENT RESTRAINT .................................
INSTANTANEOUS OVERCURRENT UNIT ............................
DROPOUT OF MAIN UNIT ......................................
LOCATION ........................................................
MOUNTING.
.......................................................
.....................................................
ADJUSTMENTS .....................................................
RATIO MATCHING ADJUSTMENT .................................
UNBALANCE CURRENT MEASUREMENT .............................
PERCENT SLOPE SETTING .....................................
OPERATION. ......................................................
TARGETS ...................................................
DISABLING OF TYPE RELAY ...............................
MAINTENANCE .....................................................
CONTACT CLEANING ..........................................
PERIODIC TESTS ..................................................
PICKUP ....................................................
HARMONIC CURRENT RESTRAINT ................................
THROUGH CURRENT RESTRAINT .................................
RENEUAL PARTS ....................................................
15
15
15
15
16
16
16
17
17
17
17
18
i
3
INTRODUCTION
3
3
4
4
4
4
STD
5
6
6
STD
7
7
7
8
8
8
MODELS
12
STD
15
B
12
STD
16
B
8
8
8
9
9
DIFFERENTIAL
9
10
10
10
11
11
11
11
MAIN
12
12
12
12
12
12
13
13
13
13
13
14
14
15
.
15
CONNECTIONS
15
16
16
STD
17
17
2
Courtesy of NationalSwitchgear.com

GEK-45307
TRANSFORMER DIFFERENTIAL RELAYS
PERCENTAGE AND HARMONIC RESTRAINT
AND
INTRODUCTION
Relays of the STD type are transformer differential relays provided with the features of percentage
restraint.
A static decision unit controls a small telephone type relay the
Percentage restraint permits accurate discrimination between internal and external faults high
while harmonic restraint enables the relay to distinguish, by the between
current caused by an internal fault.
and that of transformer Inrush.
DESCRIPTION
Each Type STD relay is a single phase unit. The Type is designed to be used for the
of two-winding power transformers and has two through-current restraint and One
current circuit.
The Type relay is designed for use with three-winding power and has three through
ent restraint circuits and one differential current circuit. It may also be used for four
protection (see Figure 9) when only three circuits require through current restraint, while the
th circuit. being the weakest, needs no through-circuit
APPLICATION
The current transformer ratios and relay taps should be selected to obtain the sensitivity
out
overload of the relay or current or the Of
efor
transformer in the various windings of the power transformer should be
the points in mind:
1.
The lower the relay tap and the lower the CT
the higher will be the sensitivity.
the lowest CT ratio and the lowest relay tap may not be compatible with of the
following restrictions. a choice is available of increasing either the CT Or the
it is desirable to increase the CT ratio in preference to the
Since the relay burden is likely to be small compared to the lead burden. increasing the
ratio tends to improve the relative CT's as a result Of the
secondary fault current and increasing the accuracy of the
The CT should not exceed the continuous thermal rating Of the CT
3. The relay current corresponding to KVA (on a forced cooled should not
twice tap value, the thermal rating of the relay.
4. The CT ratios should be high enough that the secondary currents will not the relay under
internal fault conditions (refer to RATINGS).
5. The relay current corresponding
rated KVA of the power (On Self cooled basis)
should not exceed the relay tap value selected (magnetizing inrush might operate the instantaneous
avercurrent unit). If the transformer under consideration does
not have a
the transformer manufacturer should be consulted for the "equivalent self-cooled rating that is
the rating of a self-cooled transformer that would have the
same magnetizing inrush
as the transformer being considered.
3
WITH
STDI
6
C
STD
15
C
which
provides
larmonic
ict
output
.
at
difference
in
waveform
,
magnetizing
•
*
nt
,
-
inferential
STD
15
C
relay
circuits
action
,
arential
transformers
STD
16
C
circuit
sformer
restraint
.
maximum
possibility
'
misoperation
.
selected
transformer
,
'
‘
•
'
king
thermal
:
vrr
*
nt
iollowing
ratios
ratio
selected
,
some
ratio
However
,
Where
relay
tap
.
relay
tap
,
CT
maximum
reducing
performance
of
the
CT
'
s
.
secondary
secondary
’
current
2
.
winding
.
basis
)
exceed
maximum
damage
maximum
transformer
to
self
-
cooled
rating
,
it
.
x
.
i
character
-
istics
Tht
-
irt
ructions
do
not
purport
to
COVT
oil
d
.
toih
or
variohon
.
Voquip
^
n
^
or
f
to
tho
Gantro
/
Eloctric
Cotnpony
.
Courtesy of NationalSwitchgear.com

100% Transformer KVA
(Line KY)
Actually this calculation does not mean that all windings will necessarily carry these
load currents continuously. This is only convenient of calculating the currents in
other windings In proportion to their voltage ratings. This is the requirement for selecting
the relay tap setting so that the relay will not operate for any external fault.
3. Select CT ratios so that the secondary current corresponding to maximum does not exceed
secondary thermal rating amperes). In the case where a transformer is connected to ring
bus. for example. the CT ratio should be selected so that the CT thermal rating will not be ex-
ceeded by the maximum load current in either breaker. Also select CT ratios so that the relay
currents can be properly matched by of the relay taps. (Highest current not more than 3
times lowest current).
For Wye connected CT's
Tap Current
N
For Delta connected CT's
Tap Current 100%
N
Where N is the number of CT secondary turns.
4. Check the matching of relay currents to relay taps to keep the mismatch error as as possible.
Calculate the percent of mismatch as follows: on two winding transformers, determine the ratio of
the two relay currents and the tap values
The differences these ratios, divided
by the smaller ii the percent of mismatched. The mismatch normally should not exceed 5:.
For transformers, the percent of mismatch error should be checked for all combin-
ations of currents or taps.
If taps cannot be selected to this percentage error within allowable limits, it will be
necessary to choose a different CT ratio on one more lines to obtain better match between
relay currents and relay taps.
Check to see that the sum of the relay currents that be applied to the relay for a fault at
the terminals of'the power transfoner is less 220 amperes for 1 second.
If the period
during which a fault current flows in the relay can be definitely limited to shorter time,
hiqher current can be in accordance with the relation:
(Amperes)' seconds
Also check that the sum of the multiples of tap current on an internal or fault do
exceed
CURRENT TRANSFORMER RATIO ERROR
.
CT ratio error be less than 20 percent 8 times relay rated tap Current. This
the instantaneous unit being set at its normal setting which is times tap rating. If the instantaneous
pickup is raised above this value, the 20 percent figure must be reduced as described under the
heading CHARACTERISTICS.
The calculations listed below are for the worst fault condition, as far as CT is concerned
which is an internal ground fault between the CT and the transfoner winding with none of the fault Current
through the neutral of the protected
S
GEK
-
45307
10
«
I
*
P
JT
maximum
the
a
way
the
CT
!
P
(
5
a
means
,
100
%
Ip
IpV
3
low
selected
.
between
ratio
,
three
-
wind
inq
IceeD
a
or
will
5
.
RMS
than
a
accommodated
a
*
48
,
400
x
external
not
150
.
is based
on
The
at
must
8
unit
performance
transformer
.
ipplied
Courtesy of NationalSwitchgear.com

i
,
I
i
Determine burden on each CT. using the following expressions:
a. connected CT's
2R
b. For delta CT'S
relay total burden (sea Table
N number of turns in bushing CT
bushing CT resistance per turn,
(at maximum
CT resistance per lead. (at temperature)
R control cable lead (at expected temperature)
CT current for 8 times tap setting.
8 relay tap rating
(NOTE: For the location of fault assumed. a
11
the fault currant Is by one CT. so that
and relay current are the same, regardless of whether the are connected in or
.
Determine secondary CT voltage required 8 times tap setting.
excitation curve of particular tap of current transformer determine excitation
current. this secondary
the percent error In each CT by the expression:
error
should not 20 percent on set of If it does. be to
choose a higher tap on that set of and repeat the calculations on selection of relay
mismatch error, and percent ratio error.
PERCENT SLOPE SETTING
proper percent slope is determined by the sum Of: .
a. The maximum range of manual taps and the load-ratio-control,
or tap means.
in percent.
b. The percent of mismatch of the relay taps.
The percentage slope tap should greater than the ratio Of error
smaller of the through currents. In general, if the total error current does 20 Percent.
the 25 percent tap is used.
If it 20 percent, but not 35 percent. the
the lead is used (as in for example) the percent should be about
SEK
-
45307
1
.
the
c
For
Wye
Z
-
B
Ne
+
2
f
(
EQ
.
1
)
Ohms
1000
connected
Ne
+
2
f
+
2
R
Ohms
(
EQ
.
2
)
Z
-
2
B
1000
I
)
Where
B
-
STD
expected
temperature
)
mllHohms
e
*
maximum
expected
mllHohms
f
*
bushing
maximum
resistance
*
one
-
way
c
.
Determine
secondary
x
STD
S
supplied
CT
'
s
CT
current
delta
.
)
wye
3
.
at
E
I
.
Z
s
sec
being
used
,
4
.
From
l
£
.
corresponding
to
voltage
,
E
sec
*
5
.
Determine
*
h
x
100
t
17
s
It
will
necessary
CT
'
s
.
exceed
This
any
CT
'
s
,
taps
,
required
The
changing
automatic
maximum
maximum
:
total
not
exceed
40
percent
tap
Is
used
.
current
selected
be
to
exceeds
s
1
°
Pe
tap
chosen
movable
twice
as
since
F
'
iQure
9
r
-
rpftrc
^
nt
.
If
6
Courtesy of NationalSwitchgear.com

REFER TO FIG.
I DETERMINATION OF C.T. TURNS AN0 RELAY TAP
1. Transformer and Line
2. Ip = (line
3 (line
turns
5. Max. I secondary (less than
6. 100% I secondary
CT connections
Relay Current for 1002 I Sec.
20
1.37
20
2 47
1.98
125
60
2.62
3.60
Select a relay tap for one of the line currents and calculate what the currents in other lines would
be they were increased In the ratio.
If any current is greater than root three times any other,
the 6.7 tap should be chosen for it and ideal relay taps calculated for the other lines.
9. Ideal Relay Taps (Set C = 8.7)
10. Try Relay Taps
11. Check Mismatch Error
3.31 4.70 a.7
3.24.6
Ratio of Taps on Lines B-A = 1.43 of Sec. Lines Currents
1.98
-=
1.37
1.
a.7
Ratio of Taps on Lines C-6 = 1.89 Ratio of Sec. Line Currents = 1.62
Mismatch = 3.6%
1.62
Ratio of Taps on Lines C-A = 2.72 Ratio of S C . Currents 2.63
=
(All are less than therefore. error la not
12. Check the sum of the maximum relay currents is less than amps for one and
therefore. short-time rating of relay is not exceeded.
PERCENT RATIO ERROR
ASSUME (all measured at their expected
One-way CONTROL CABLE RESISTANCE
=
CT;
c
Bushing resistance per lead
18.6
.
1.
BURDENS ON CT's
USING 1
OR 2 from page 5.
a. A. Z
2 l
(2.0
000
0.312 0.205 l 1.085
l
+ 0.0% l 0.136 + 0.60
c. Line C. Z = 2 (0.046) +
100 +
= 0.0% l 0.180 0.568
= 0.833
GEK
-
45307
EXAMPLE
17
SETTINGS STD
A
C
B
19.7
3750
/
VIT
3
.
100
%
Ip
«
3000
/
V
.
4
.
Assume
CT
1
?
7
KV
)
49.5
Max
.
KV
)
15.7
39.6
(
N
)
0.98
»
»
5
a
)
0.79
1.58
2.08
v
•
r
^
Delta
Delta
Wye
7
.
8
.
1
f
same
new
8.7
4.6
1.44
Ratio
377
1.44
1.43
,
0.7
%
Mismatch
43
4.6
1.89
-
1.82
8.7
Line
n
2.72
-
2.63
3.4
%
Mismatch
excessive
)
mismatch
5
%
;
220
second
,
that
II
temperatures
)
maximum
(
R
)
.
284
ohms
4
mllHohms
resistance
per
turn
(
e
)
»
;
e
)
-
2.5
"
e
)
-
2.3
"
f
)
-
75
"
f
)
-
52.5
"
(
f
)
*
Bushing
A
H
D
B
<
4
A
CT
B
"
4
!
C
“
EQ
.
EQ
.
•
(
0.156
)
x
75
)
(
20
x
*
,
)
Line
+
2
(
.
284
)
1
0.568
-
(
2.1
x
52.51
(
20
x
2.51
©
.
sea
k
.
UlT
*
2
*
©
-
'
1
S
5
IDDO
0.568
*
(
60
x
2.3
)
+
(
2
x
18.6
)
0.568
00
7
Courtesy of NationalSwitchgear.com

2. 1.085 0.8 0.833
3. a 36.8 69.6
ES CT required
27.8 29.b 58.0
required, excitation
curve
1.00
50
Ratio Error
3.4% 136%
Exciting current on line is high;
should try higher tap on CT to improve CT
IA REPEAT CT TURNS AND RELAY TAP SETTING
1.
Try CT turns (necessary to change C
also for proper matching)
3. I secondary
Relay Current.
Ideal Relay (SET C 8.7)
6. Use Taps
7.
Mismatch error is less than
Total Burden for 60 Cycle Relays
15.7 39.6 125
0.79
1.37
4.40
4.6
40 80
0.99 1.56
0.99 2.70
TABLE I
IIA REPEAT PERCENT RATIO ERROR
1. Burden on CT's
Line A. Z 0.192 0.205 0.965
Line 0.156 + 0.568 0.912
Line Cm Z 0.096 + 0.226 0.890
2. Impedance.
3.
8 Times Tap, Amperes 36.8 25.6
CT voltage required 35.6 23.4
5. required, from excitation curve
1.1 0.25
6.
of Ratio Error
3.1%
1 .
Percent Error is less than 20%. so CT taps and Relay taps are satisfactory.
69.6
61.9
0.17
0.3%
III PERCENT SLOPE SETTING
1. Assume load ratio. control maximum range
2. Relay Tap mismatch, IA above (Lines
10.0:
4.6:
Use 25% tdp.
RATINGS
14.6%
---
Continuous rating The through current transformer differential transformer Will stand
twice value for any of taps or they will stand twice tdp value if all but one of
carry zero current the full restraint current. equal to twice tap
the current transformer.
GE
<
-
45337
A
B
C
ohms
Impedance
,
T
imec
anoeres
25
.
*
?
*
a
n
(
12
)
4
.
voltage
from
IE
.
5
.
0.5
6
.
0.8
%
*
B
too
performance
.
1002
Ip
2
.
20
100
?
4
.
Taps
5
.
3.19
8.7
a
3.2
8.7
5
S
MIN
.
P
.
U
.
AMPS
i
BURDEN
OHMS
(
B
)
8
X
TAP
AMPS
STD
TAPS
AMPS
!
0.87
0.180
0.156
0.140
0.120
0.112
0.096
0.088
0.048
23.2
2.9
0.96
25.6
>
.
2
1.05
28.0
3.5
1.14
30.4
3.8
1.26
33.6
4.2
1.38
36.8
4.6
1.50
40.0
5.0
2.61
69.6
8.7
0.568
*
s
0.188
+
B
,
Z
*
S
0.568
=
S
Ohms
.
965
.
912
.
890
(
I Z
)
E
$
ec
«
4
.
IE
0
%
l
A
-
B
)
from
MODELS
12
STD
15
C
AND
12
STD
16
C
and
Current
comfcinati
on
tap
tfie
,
res
-
value
,
flows
through
traint
windinqs
differential
and
8
Courtesy of NationalSwitchgear.com

amperes for second measured in the primary Of any
nigher may be applied for shorter lengths of time in accordance the
1%
where:
I current amperes
t time in seconds
Short Time (electrical)
For the and the Of the multiples Of tap fed
to the relay from the several sets of current transformers should not exceed 150. These multiples should
be calculated on the basis of fault current.
This limitation is a result of the voltage
of the rectifiers in the through current restraint
Note that in Fig. 9 external fault
current can flow through circuit breakers and 52-2 without being limited by the Impedance.
TABLE II
2.0
0.6 ,
0.2
Tap
Tap
Tap
D-C Resistance 0.13
0.6 Ohm
7
Carry Continuously
0.5 Amps
1.5 Amps 0.25
carry for 4 0.5
----
Carry 10 Amps for 30
4
0.2
AUXILIARY RELAY CONTROL CIRCUIT
The and relays are available for use with 48. 125, and 250 d-c voltage. A
with small links located on the front of the relay enables
the selection of one of these voltages.
The relay is provided with two open contacts connected to a output circuit. The current
closing rating of the contact is 30 amps for voltages not exceeding 250 volts. If more than one
break& is to be tripped or if the tripping current exceeds 30 amperes. an auxiliary relay must be used
with the relay. the breaker trips. it is necessary that the tripping circuit of these
be de-energized by an auxiliary switch on the circuit breaker by other
reset relay is and normally used.
CHARACTERISTICS
PICKUP AN0 OPERATING TIME
The operating characteristic Is shown in Fig. 1.
The curve for various percentage the
percent slope versus the through current flowing in the
The percentage slope is a figure
given to a particular slope tap setting and indicates an approximate pickup at
zero restraint is 30 percent of tap value (see Table III). The dropout time the
operating current is reduced from any value above pickup to zero is less than 25
of the operating time of the main unit and of the instantaneous unit are shown in Fig.
plotted against differential current. The main operating time includes auxiliary unit operating time.
OVERCURRENT UNIT PICKUP
The unit is adjusted to pickup when the differential
‘8 times the ampere produced by rated tap current flowing in that For example:
only one supplies current. and the tap plug for the CT is in the ampere tap, 40
amperes are required for pickup.
This pickup value is on the A-C Of current
only, since the differential current transformer in the relay a half
cycle of any d-c present.
GEK
-
45307
*
transformer
z
*
with
Short
Time
Rating
(
theflW
?
che
type
STD
relay
,
following
equation
:
•
•
48.400
220
1
i
-
currents
s
=
1
current
STD
15
C
STD
16
C
both
sum
RMS
symmetrical
circuit
.
rating
transformer
52
-
1
TARGET
AND
SEAL
-
IN
UNIT
Amp
Amp
Amp
Ohms
Ohms
Amps
Secs
.
Secs
.
30
Amps
Secs
.
Secs
.
Secs
.
control
STD
15
C
STD
16
C
>
»
iate
STD
common
circuit
relays
automatic
provisions
.
A
manual
STD
After
or
recommended
slopes
shows
transformer
.
slope
characteristic
.
when
milliseconds
.
approximately
2
,
Curves
unit
current
transformer
ampere
-
turns
are
tap
.
overcurrent
turns
5
CT
When
trans
-
based
component
produces
only
former
output
(
offset
)
component
9
Courtesy of NationalSwitchgear.com

It should be recognized that pickup current flows not only through current transformer
but also through one of the primary windings of the through current restraint.
However, compared to the operating energy, this quantity of restraint is so small it may assumed
to be zero.
CURRENT RESTRAINT CIRCUIT
A full wave rectifier receives the output of the secondary of each through current restraint
transformer. In the relay. the d-c output of all three units are connected in The total
output is directed to the percent slope rheostat located on the front of the relay. By means of'
adjusting the rheostat, the percent slope may be varied 15 to 40 percent. The is put through
an isolatinq transformer, rectified and to the solid state amplifier which the
telephone tyoe relay.
DIFFERENTIAL CURRENT CIRCUIT
The differential current secondary supplies the instantaneous unit the
operating signal to the solid state amplifier through a series tuned circuit; and the harmonic restraint
isolating transformer through a parallel resonant filter. The operating and restraint currents are each
rectified by a full wave bridge prior to being supplied to the sensitive amplifier.
The series resonant circuit is made up of a microfarad
capacitor (Cl) and a reactor
which are tuned to pass currents of the fundamental system frequency and to offer high impedance to
Currents of other frequencies.
Resistor is connected in the a-c side of operate
and can be to give the desired amount of operate current.
The output of the is applied
the operating of the sense amplifier.
The parallel resonant trap is made of a 15 microfarad
l Pyranol capacitor and a reactor
which are tuned to block fundamental frequency currents while allowing currents of
to pass with relatively little impedance. Resistor R2 is connected in parallel on the a-c side of the
harmonic restraint rectifier, and can be adjusted to give the desired amont of harmonic restraint. The
output of the rectifier is paralleled with the through current restraint currents and applied to
restraint of the sense amplifier.
It will evident that if the differential current applied to the relay is sinusoidal and of system
will flow mostly in the operating circuit and hence cause the relay to yield an output.
if. however. the differential circuit contains than a certain percentage of the relay will
be restrained from by the harmonic currents flowing in the restraint
A resistor connected across the secondary of the differential limits
any momentary high voltage peaks which may thus protecting the rectifiers and capacitors damage
without materially affecting the characteristics of the relay.
OVERCURRENT UNIT
The instantaneous unit is a hinged armature relay with a self contained target indicator. On
heavy internal fault currents.
this unit will pick up and the trip circuit. The
unit target will be exposed, to indicate that tripping was through the instantaneous unit.
Because of saturation of the CT's and relay transformers at high fault currents, it is impossible that
less operating currents will be provided from the differential-current than the percentage
slope tap imply, and harmonic restraint will be provided than the actual harmonic content of the
would supply.
As a result, conditions of a high internal fault current, the unit
may be falsely restrained. Tripping is assured, however, by the overcurrent unit operation. Pickup
set above the level of differential current produced by maximum magnetizing inrush current. Figure 2
the relative levels of pickup and speed of operation of the unit and the overcurrent unit.
l Trade-Mark of the General Electric Company
GEK
-
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OPERATING UNIT
The primary functioning of the relay is a state amplifier whose controls a
simple telephone relay.
The sense ampllfler is shown In Fig. 10 and as a large rectangle. The amplifier
consists of many electronic components mounted on a printed circuit card in the top half of the relay.
This printed card is installed in an eight-prong printed card design base. This
Is adjusted prior the factory and should require no further attention. A schematic of this
card is shown in Fiq. The telephone-type relay is mounted vertically in the mid-section of the relay.
It too has been carefully adjusted at the factory and should require no further attention.
If this small
relay has been disturbed, refer to the section under adjustment.
TARGET AND SEAL-IN
a target and seal-in unit mounted on the top left of the relay. This has Its coil in
series and its contacts in parallel with the main contacts of the telephone-type relay. the
type relay contacts close, the seal-in unit operates; raising its target into vision and sealing around
the telephone type contacts. The target of this unit will remain exposed until released by pushing a
button beneath the lower left corner of the cover of the relay case.
The case suitable for surface or semi-flush panel mounting, and an assortment of hardware is pro-
vided for method. The cover attaches to the case, and carries the target reset mechanism for the
indicator and instantaneous unit. Each cover screw has provision for a sealing
The case has studs or screw connections at the bottom for the external connections. The
connections between the relay unit and the case studs are made through spring backed contact finger mounted
in stationary molded inner and outer blocks between which rests a removable connecting plug which completes
circuit. The outer block, attached to the case, holds the studs for the external connection, and the
block has terminals for the internal connections.
The relay mechanism is mounted in a steel framework called the cradle and is a unit with all
leads terminating at the inner block. This cradle held in the case with a latch at the top and
a guide pin at the back of the case.
The case and cradle are so constructed that the relay
cannot be inserted in the case upside down.
The connecting plug. besides the connection
between the blocks of the cradle and case, also locks the latch In place. The cover. which fastened to
the case by thumbscrews. holds the connecting plug in place.
To draw out the relay unit, the cover is removed and the plug is drawn out. Shorting are provided
in the case to short the current circuits (see Fig. 6). The latches are then released and the
relay can be easily drawn out.
A separate testing plug can be inserted in place of the connecting plug to rest the relay in On
the panel either from its own source of current, or from other sources. Or, the relay unit can be drawn
out and replaced by another which has been tested in the laboratory.
RECEIVING, HANDLING OR STORAGE
These relays, when included as a part of a control panel will shipped In cartons designed
protect them against damage;
upon receipt of a relay, examine It for any damage in
transit.
If injury or damage resulting from rough handling is evident. file a damage claim at once with
the and promptly notify the nearest General Electric Apparatus
Reasonable care should be exercised in unpacking the relay in order that none of the parts are
or the adjustments disturbed.
If the relays are not to be installed they should be stored in original cartons in
a place that is free from moisture, dust and metallic chips. Foreign matter collected on the outside of
case may find its way inside when the cover is removed and cause trouble in the operation of the relay.
GEK
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Courtesy of NationalSwitchgear.com