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Relay Calibration - IDMT
How to spot check the relay
calibration results?
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Pre-Requisite
You are an electrical engineer or a charge man or a wire man or a tester or an
electrician or a practical student or just anyone:
Who would like to know more about a typical Suruhanjaya Tenaga (ST) relay calibration certificate
results
While waiting for the electrical service tester complete the relay calibration, how can you be sure if
the tester is doing it right i.e. if the results are right. “Betul ke inject current banyak ni, operating
time dia secepat ni?”
As a pre-requisite, you must have the following knowledge:
a. Differences of IDMT, DT, Hi-Set
b. Curve type whether it’s IEC, ANSI, IAC or others
c. Well not really down to the details but if you know the curve type, PS, TMS and ask the right
question – you can know whether test is done right.
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CT Details
1. Primary Current
OCEF Relay 2.
3.
Secondary (1A or 5A)
Note if separate CT used for
EF i.e. ZCT, CBCT, Neutral CT
Certificate Relay Details
1. Protection Type – OC, EF, OL,
Others
2. CT Input 5A or 1A or
Relay Settings interchangeable/ can be set
1. Sec. Current PS/ % PS
2. TMS
3. Curve Type – NI/SI, EI, VI, LI Test Settings
PS – Plug Setting 1. Good Practice To Record this
TMS – Time Mult. Setting test settings
2. Common mistake: Settings left
as per test settings
Operating Time Test (IDMT)
1. Test current at 1.3x, 2x, 3x
PS (4.88A, 7.5A, 11.25A)
Stability Test
2. Operating time (refer to
1. To know if any CT polarity is incorrect.
curve type, curve
2. Example you inject at R and N phases.
standard-IEC, ANSI, IAC)
If CTs’ polarities are correct, current
summation = 0. If not, zero seq. or
Operating Time Test (Hi Set) residual current is not 0.
1. PS for Hi Set 3. For differential protection, stability
2. Op. Time depends on relay. tests include in zone and out zone
Typically 40 – 50 msec or use of DT. stability test.
Trip Voltage Who can test?
1. Typically 240VAC, 110VDC, 24VDC 1. Only Electrical Service Contractor (ESC) can perform and
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for the shunt trip/ UV trip coil approve relay calibration.
2. Some use capacitive trip coil – 2. Other than relay calibration, ESC scope include
doesn’t need external power. maintenance, repair, overhaul, service, test and
commission any installation or equipment and locate
cable faults (Reg. 71 (1), ER 1994)
Brief Intro on IDMT/ Curve Type
PENING SUDAH TENGOK SEMUA
NI. JOM PI TENGOK EXCEL PLAK.
V = I / I pu = PSM = Plug
D = TDM = M =TMS =
Setting Multiplier
Time Multiplier Setting
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IDMT SPOT CHECK
1. Useful to counter check ON THE SPOT results of electrical service contractor during commissioning
or calibration of the relays.
Contoh Situasi Utk Pakai Skil Ni
2. Applicable only to IDMT relays.
You: Tester, meh sini tengok result
calibration
Tester: Ni bang.
You: (Oh ni PS=5A, TMS=0.83. Curve
plak IEC EI). Tadi bro, inject 3x (15A)
IEC dapat berapa trip time?
Trip time = PSM required to inject to get Tester: Hmm… dalam 7.5 sec.
TMS
10*TMS (Sec) 10*TMS trip time
You: Betul ke ni? Bukan patutnya 8.3
Standard Inverse (SI or NI) = 0.20 2.00 2.00
sec ke?
Very Inverse (VI) = 0.20 2.00 2.35
Tester: (Amik calculator) Betul la
Extremely Inverse (EI) = 0.20 2.00 3.00
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silap. Jap saya cek… silap key in TMS
Trip time = PSM required to inject to get
TMS la bang (Power plak client ni)
100*TMS (Sec) 100*TMS trip time
Long Time Standard EF (LTSEF) = 0.20 20.00 2.20
Thank you for listening. Please don’t forget to:
a. Subscribe my Youtube Channel: Crux of EE Electrical Engineering
b. Like my Facebook page: Crux of EE
c. Visit my website: www.cruxofee.com
d. Any questions, you can email to: cruxofee@gmail.com
Thank you
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