TRANSFORMER CONDITION ASSESSMENT

Project No: File: Valco Aluminium_6997140 Page 1 of 10

DOBLE ENGINEERING AFRICA

TRANSFORMER DIAGNOSTIC TESTING AT VALCO ALUMINIUM

This report was prepared on the 25th May 2015 by:

Kamendren Govender

Principal Engineer

CLIENT: VALCO ALUMINIUM

TRANSFORMER CONDITION ASSESSMENT

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REPORT DETAILS

CLIENT Volta Aluminium Company Limited

ADDRESSEE

SITE Line 1

JOB DESCRIPTION Transformer Condition Assessment

REPORT PREPARED BY Kamendren Govender

DATE REPORT COMPLETED 25th May 2015

REPORT AUTHORISED BY Luwendran Moodley

CLIENT ORDER NUMBER

Copyright © 2007 Doble Engineering Africa Limited

All rights reserved. No part of this publication may be produced stored in a retrieval system or transmitted in any form by any means electronic mechanical photocopying recording or otherwise without the prior written permission of Doble.

Indemnity This document may not be distributed or used outside the client for whom it is prepared except with written authorization from Doble. Doble disclaims all liability for any loss damage injury or other consequence whatsoever arising from any unauthorized use howsoever caused including any such resulting from error omission or negligence in its application.

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Table of Contents 1. Executive Summary...............................................................................................4

1.1. Findings ..............................................................................................................4 1.2. Recommendations ..............................................................................................4 2. Analysis and Observations ......................................................................................5

2.1. Transformer Details ..........................................................................................5 2.2. Condition Analysis ...........................................................................................5 2.2.1. Electrical Test Findings ......................................................................................5

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1. Executive Summary

1.1. Findings

Doble Engineering Africa was requested by Valco Aluminium to perform diagnostic tests and analysis on a transformer based on electrical tests. This report covers the final findings based on our studies of the transformer with serial number: 6997140 manufactured by Westinghouse Electric. All winding power factor and capacitance results are within acceptable limits. From our experience the high power factors on the LV1 and LV2 windings does not allude to insulation deterioration but rather the effect of surge capacitors. The excitation currents are within acceptable limits.

The ratio test revealed no significant concerns with all ratios being within the acceptable limits. The DC winding resistance tests results are within acceptable limits. The Sweep Frequency Response Analysis (SFRA) revealed no winding deformation on the 13.8/0.39 kV windings for all phases. The moisture content is at unacceptable values and indicates insulation contamination. The acidity is at acceptable values.

The DGA signature is indicative of a normal operating transformer.

1.2 Recommendations Doble Engineering recommends the following: Drying techniques (such as oil purification, low frequency heating, etc) Furan measurements to assess the condition of the insulation

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2. Analysis and Observations

2.1 Transformer Details

The transformers details are given in Table 1.

Table 1: Transformers Details

Substation Line 1

Unit R15

Serial Number 6997140

Manufacturer Westinghouse Electric

Year of Manufacturer 1965

Voltage 13.8/0.39/0.39 kV

VA Rating 16.45 MVA

2.2 Condition Analysis

2.2.1 Electrical Test Findings

2.2.1.1 Windings Insulation

Results and Analysis The winding power factor values are given in Table 2.

Table 2: Winding Power Factor and Capacitance Test Results

Measured Voltage (kV) Power Factor (%) Capacitance (pF)

HV winding to earth 8 0.35 5 017.75

Between HV and LV1 winding 8 0.27 5 008.66

LV1 winding to earth 0.2 4.13 4 613.23

Between LV1 and LV2 winding 0.2 0.28 5 008.96

LV2 winding to earth 0.2 2.78 4 394.90

Between LV2 and HV winding 0.2 0.19 5 043.41

All winding power factor and capacitance results are within acceptable limits. From our experience the high power factors on the LV1 and LV2 windings does not allude to insulation deterioration but rather the effect of surge capacitors. 2.2.1.2 Excitation Current Tests Results and Analysis The results from the excitation current tests are shown in Table 3.

Table 3: Excitation Current Test Results

Tap Red Phase Yellow Phase Blue Phase

Current (mA) Loss (W) Current (mA) Loss (W) Current (mA) Loss (W)

5 748.11 5 432.61 643.22 4 727.24 620.49 4 521.13

The excitation currents are within acceptable limits.

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2.2.1.3 Ratio Test Results and Analysis

The results of the ratio test for each phase and tap position shall be within 0.5 % of the nameplate data. The results from the ratio tests are given in Table 4.

a) HV to LV Winding

Table 4: Ratio Test Results

Ratio Red Phase Yellow Phase Blue Phase

H - 11 7.73 7.39 7.40

H - 13 7.73 7.38 7.41

H - 8 7.88 7.43 7.58

H - 10 7.86 7.42 7.58

The ratio measurements are within acceptable limits. 2.2.1.4 DC Winding Resistance

Results and Analysis The DC winding resistance tests were performed on all windings and are shown on Tables 5, 6 and 7.

a) HV Winding Table 5: HV DC Winding Resistance Test Results

Tap Red Phase Yellow Phase Blue Phase

Resistance (m) Resistance (m) Resistance (m)

5 89.67 90.29 90.50

The DC winding resistance test results are within acceptable limits. b) LV1 Winding

Table 6: LV1 DC Winding Resistance Test Results

Tap Red Phase Yellow Phase Blue Phase

Resistance (µ) Resistance (µ) Resistance (µ)

5 182 182 173 The DC winding resistance test results are within acceptable limits.

c) LV2 Winding Table 7: LV2 DC Winding Resistance Test Results

Tap Red Phase Yellow Phase Blue Phase

Resistance (µ) Resistance (µ) Resistance (µ)

5 187 179 185

The DC winding resistance test results are within acceptable limits. 2.2.1.5 SFRA Test

Results and Analysis

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The results from the SFRA tests are given in Figures 1 to 3.

a) HV Winding Open Circuit

Figure 1: HV Winding Open Circuit

The comparison between the phases finds that the responses demonstrate a characteristic pattern and has good correspondence across the entire frequency range. These responses do not indicate winding deformation

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b) LV1 Winding Open Circuit

Figure 3: LV1 Winding Open Circuit

The comparison between the phases finds that the responses demonstrate a characteristic pattern and has good correspondence across the entire frequency range. These responses do not indicate winding deformation

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c) LV2 Winding Open Circuit

Figure 3: LV2 Winding Open Circuit

The comparison between the phases finds that the responses demonstrate a characteristic pattern and has good correspondence across the entire frequency range. These responses do not indicate winding deformation

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2.2.1.6 Oil Analysis

a) Moisture Content

The moisture content (39ppm) is at unacceptable values and indicates insulation contamination. b) Acidity The acidity content (0.03) is at acceptable values.

c) DGA

Figure 4 below shows the DGA history of the oil.

Figure 4: DGA Signature

The DGA signature is indicative of a normal operating transformer.