Transcript
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I
"UNION'' SERVICE SPEC:lrlCATION .
.
: UNION SWITCH
.. o·· VISION
OF
a
NUMBER
2735
SIGNAL .; •••• IW'IIIVUB, PL
WESTINGHOUSE
A IR
BI A JC E
COMP AH Y
"TH" THERMAL REIAY
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1. Foreword.-
This service specii'ication covera_the repair and adjustment ot "THu thermal relays. '
Style "TH" thermal relays are
.
limited to 1 front£!:. 1 back contact only.
They have been
furn1she,~ with delay times (time from the instant power is applied until the front contact closes) of from 5 seconds to 30 seconds,
Eithe:r alternating or direct current can be used
for service or testing.
The relay is not designed for contin-
uous energization., so it is imperative that pover be cut off as
soon as the front contact is closed or the back contact is opened.
This can best be done by operating a neutral relay from
t'lle thermal relay contact and using the neutral relay to take the power off t.he hes. ter unit,. 2. General -Design.
The operation of the "TH" relay depends upon the dii'ference
or
temperature coefficients
or
expansion
tne bimetallic thermal material.
or
two metals comprising
In the relay with the normally
open contact, the driver (See Fig.1) which is the piece of bimetallic thermal strip on which the heater coil is wound., is
.
arranged with the high temperature coefficient side (brass) away from the direction . When· the heater coil is Rev. Sheet 4
4/B/40
or
motion necessary to close the contact •
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U.S.& S.
Service Spec. #2735 Date: 6~18-35
energized, the difference in the expansione,of the twe metals causes a curling or bending action of the driver..
The o·ther piece of bimetallic
strip, called the ..compensator, has the high temperature co_efficient side in the opposite direction, thereby tending to oppose the movement of the driver.
The driver and compensator are coupled by means of a link
and pin assembly. The two bim.etallic elements are so selected that with the relay deenergized., the contact members remain in practically fixed relationship to each other regardless of the surrounding temperat,ures . .
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F'ig. 1.
U.S.;&
S.
-3-
Service Spec. #2735 Date: 6-18-35 ·
Relaye · wi-th normally closed back contacts have the thermal· metal of the driver and -compensator assembled with the high temperature
coeff 1c1ent · sides reversed from the normally open front contact rela,ys descrtbed in the foregoing. Time adjustment is made by changing the adjustable contact position by means of the adjusting screw.
No provision has been made
for external time adjustments so that the delay time can only be changed or adjusted in the shop by br~aking the seal and-opening the relay .. Thg heater consumes approximately 10 watts power while the relay is energized.
The design of the heater and thermal strips is such that
satisfactory vol~ge-time characteristics will be obtained if the relay is operated within reasonable limits of its normal rated voltage.
3. Mechanica.l Inspection The driver and compensator elements should be aligned, and the pins so applted that there is no binding in the pin and link assembly. The-flexible connectors should be neatly dressed so that they will not touch the relay cover glass or any metallic parts of the relay. The contacts should be so adjusted that both silver buttons hit the flat silver tip at the same time~.
4. Elect~ical Teet. All' tests of the relay time should be made with the relay in the vertical position with the glass case securely fastened. The test.and adjustment outlined below is for the relay with normally open contact and applies to the relay with normally closed contacts, except that in the latter case the time delay required to open the contact is measured$
u . s.& s.
Service Spec. #2735 Date: 6-18..-35 Rev: 4-a:..40
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A testing circuit should be used which employs an ordinary-
acting neutral relay, energi"z,ed to at. least twice its pick-up value
and controlled by the
11
Proper ne'l;ttral relay contacts
TH 11 relay contact.
should be· used. and the circu1.t so arranged that the therma1·relay neater is deenergized at the end of its time interval ..
The relay should be adjusted and tested at its normal voltage 1 vhich is standard on the relay name Qlate. At this energization the delay time (interval from instant power is applied until the front contact closes), should be within 5% of its vhich is also stamped on the name plate. rated value/ Delay times at voltages 1oi above and below rated, should come within lO'Jt of the values given in Table #1.
A atop watch can be
used to measure the delay time providing care is taken to see that the stop watch is started at the moment energy is applied to the relay and is stopped at the same time the thermal relay contact closes to pick up the neutral.relay.
At least 5 minutes time should elapse between teats
of' delay time to be certain that the relay has cooled to room tempera-
ture and that full front contact time will be obtainedo The adJu.sting screw lock nut should be tightened before the :t'inal time tests are made.·
TABLE #1. in
Dela:y: Time
At Normal Rated Voltage
5 Sec. 10
"
Seconds,,
minimum Voltage (90{ Normal)
At maximum
At
Voltage (llOt Normal)
6 Sec. 12
"
4.25 Sec. 8.5 »
13 15
tt
16.5
tt
20
II
10.5 12.5
30
"
40
tt
25.0
Written By
~
N.c..~.~ ?/7-3sAPPr'OVed
Checked B;~~-4h~WjG,1?- 5"
3
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Date_~_B:.ZS.:: ___ _
