Winding Resistance

 

 

HV Transformer/I & QC

Department/Section: Module No:

Issued By: Work Instruction No.:

Issuance Date:

WI-I&QC-02   WI-I&QC-02

Superseding Date:

M OF WIIN ME EA AS SU UR RM ME EN NT T O F W ND DIIN NG G  R RE ES SIIS ST TA AN NC CE E 

02 01 REV

Date

Nature of Change

Pr ep ar ed B y

Ch ec k ed B y

Ap p r o ved & Co n t r o l l ed B y

Name

 Abdul Rehman

Name

Raza Raz a Aftab / Muhamma Muhammad d Shafiq

Name

Jahanzeb Ahmad

Department

I & QC

Department

I & QC

Department

I & QC

Designation Signature

Engineer

Designation Signature

Sr. Enginee Engineerr / Test Field Field Eng Engineer  ineer 

Designation Signature

Manager 

Note: Copying of this document is strictly forbidden. Proprietary data. Company confidential. All rights reserved.

 

 

MEASURMENT OF WINDING RESISTANCE WORK INSTRUCTION WI-I&QC-02

1.0

Revision: 00 

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PURPOSE

The purpose of this document is to provide the guidelines to the Testing Engineer to check whether the winding joints are in order and the windings are correctly connected. Moreover resistance is needed in connection with the load loss measurement, when the load losses are corrected to correspond to the reference temperature. 2.0

SCOPE

This instruction applies to the in-house & final testing of the HV Transformer. 3.0

RECORDS

Following items are recorded in the test reports: 1. Connection terminals between which the resistance is measured. 2. Tapping position. 3. Winding temperature at the time of measurement (if ambient equals to winding & oil temperature then winding or oil temperature can be taken). 4.0

ASSOCIATED DOCUMENTS DOCUMENTS

The standard applicable for this test is IEC 60076-1. 5.0

DEFINITIONS

Resistance

6.0

 Always defined as the D.C. D.C. resistance (active or actual resistance resistance in ohms). RESPONSIBILITY Test will be performed under the supervision of Testing Engineer/Sub Engineer of I & QC section of HV Transformer department. 

7.0

EQUIPMENTS/INSTRUMENTS

Following equipments/instruments are required to perform this test: - Multi-amp  Transformer Ohmeter Megger-USA make or equivalent, 240 V, 50/60 Hz and 350 VA.

 

 

MEASURMENT OF WINDING RESISTANCE WORK INSTRUCTION WI-I&QC-02

8.0

MEASURING CIRCUIT

9.0

SAFETY REQUIREMENTS

Revision: 00 

Page 3 of 4 

1. The connecting leads should be tightly clamped. 2. Transformer Ohmmeter should not be disconnected while the red warning light is on and current is flowing in the winding. 3. Proper ventilation should be provided to the heat sink, especially at high current setting and long duration. 4. Proper current selection and measuring range should be selected. selected. 5. Accidents of any kind s should hould be reported immediately.

 

 

MEASURMENT OF WINDING RESISTANCE WORK INSTRUCTION WI-I&QC-02

10.0

Revision: 00 

Page 4 of 4 

INSTRUCTIONS Resistance measurement by Volt-Amp ere Method Method

The test leads are connected to the terminals of the winding whose resistance is to be measured. A suitable value of current is allowed to flow in the winding by varying the series resistor. Simultaneous values of the voltage and current are taken. Their ratio gives the required resistance of the winding. The temperature of the winding (assumed to be the same as the average oil temperature) is recorded. Resistance measurement by Transform er Ohmm Ohmm eter.

The leads of the instrument are connected to the winding whose resistance is required. The meter is charged, keeping it on the appropriate current range. After the current settles down, during which the display is blank, the resistance is displayed on the screen directly, along with the proper unit i.e. Ω or mΩ. 11.0

CACLULATIONS Winding Resistance temperature dependence:

The winding resistance varies strongly with the temperature, therefore ohmic/d.c. resistance at reference temperature is computed as follows: R2 = R1 x (C+θ2)/(C+θ1) Where: R1 = Resistance at temperature

θ1 

R2 = Resistance at temperature θ2  Reference Temperature (usually 75°C) θ1 = Measured Temperature C = Material constant (for copper 235 & for aluminum 225)

θ2 =

12.0

TOLERANCES

No tolerance specified in IEC 60076-1. However, Internal tolerance limit is + 10% against the calculated values.