Which Test Set Issue1

Introduction

The protection engineer of today has a wide variety of test sets available at their disposal for their secondary injection testing needs. Much like motorcars they range greatly in performance and functionality. Ranging from the Volkswagen (Sverker and T&R) sets to the higher end Lamborghini (RES-­‐APTS) & Ferrari (Omicron) – Priced accordingly! Without question the Omicron & APTS test sets tower above the lower end Sverker and T&Rs in terms of functionality. With their multiple variable current & voltage outputs, customizable test procedures and multiple input/output contacts. They are unparalleled when it comes to testing modern electronic relays, transformer differential & modern distance protection schemes. However, can we rely on these test sets when it comes to testing the humble old Electro-­‐Mechanical (EM) Current Driven Induction Disk Relay? Why should testing EM current driven relays cause issue for concern? Well using a test set out of the box to inject such a relay, especially a high impedance current relay, causes the output waveform of the test set to be distorted. The cause of this distortion is the generation of Harmonics. A Harmonic is a sinusoidal component of a periodic wave having a frequency that is an integral multiple of the fundamental frequency. For example the UK mains frequency of 50Hz would have a 3rd Harmonic of 150Hz a 5th Harmonic of 250Hz etc…. These Harmonics superimpose themselves upon the natural sine wave. This imposition summates with the fundamental sinusoidal test set injection signal to produce a distorted waveform (figure 1).

(Figure 1 – the distortion of a sine wave by impose harmonic content)

Sometimes the distortion is so severe that the timing tests we carry out on the relay are no longer reliable. We therefore need to consider the magnitude of waveform distortion when performing secondary injection timing tests upon EM protection relays. We are able to quantify & compare the magnitude of the sine wave distortion using a standard known as the Harmonic Distortion Factor (HDF). This factor is an Institute of Electrical & Electronic Engineers (IEEE) Standard -­‐ 519-­‐1992, defined as: HDF = Square Roof Of (sum of squares of amplitudes of all harmonics) x 100%

(square of amplitude of fundamental) This report will examine the HDF experienced by a variety of test sets & filter configurations. We also see how the distortion impacts upon the secondary injection timing results.

The Testing From practical protection testing experience it has been observed that the 1A CDG16 Induction Disk Earth Fault Relay causes the most severe secondary injection testing sine wave distortions & recorded operation timing errors. It was therefore decided that the CDG16 would be an ideal relay to utilise in the test set evaluation tests. The relay was set to the minimum setting, I.E 0.1A Minimum Operation/Creep Current with a Time Multiplier (TM) of 1.0. The relay was then injected with a variety of test sets currently employed within Electricity Northwest. A variety of configurations were employed with the injection procedures, such as no waveform filtration, primary and secondary injection resistance, & secondary current filtering with the T&R 100AD filter (appendix A). The operating time & waveform characteristics we recorded over the injection cycle for each configuration of a 2x operation current timing test (0.2A Injection). The injected current level was set using a calibrated external Fluke 289 multimeter connected directly in series with the relay coil (Not the integral test set meters). The waveform was recorded on a calibrated Dranetz PX5 power monitor using a clip a 0-­‐10A 2510 clip-­‐on ammeter & direct voltage sensing.

Note: The ideal/theoretical operating time @ 2x (1.0TM) should be 10.03 sec

Results The following secondary injection configuration waveforms & timings were evaluated:

• Test 00 – T&R 100ADM – No Filter Op Time @ 2x = 14.78sec

• Test 01 – T&R 100ADM + 100ADM Filter

Op Time @ 2x = 10.35sec

• Test 02 – Sverker 760 – No Filter Op Time @ 2x = 15.32sec

• Test 03 – Sverker 760 + Secondary Resistors (126.5 OHM)

Op Time @ 2x = 13.69sec

• Test 04 – Sverker 760 + Primary Resistor (100 OHM) Op Time @ 2x = 15.27sec

• Test 05 – Sverker 760 + Primary (100 OHM) + Secondary R (126.5 OHM)

Op Time @ 2x = 13.44sec

• Test 06 – Omicron 256 (280VA @7.5A 40V RMS Output / No Filter) Op Time @ 2x = 10.67sec

• Test 07 – Sverker 760 + T&R 100ADM Filter

Op Time @ 2x = 10.31sec

• Test 08 – Sverker 650 – No Filter Op Time @ 2x = 15.28sec

• Test 09 – Sverker 650 + T&R 100ADM Filter

Op Time @ 2x = 10.50sec

• Test 10 – APTS – 3 Phase (No Filter) Op Time @ 2x = 11.80sec

• Test 11 – APTS – 1 Phase Parallel (No Filter)

Op Time @ 2x = 15.08sec

• Test 12 – APTS – 1 Phase Series (No Filter) Op Time @ 2x = 9.85sec

Note: The sampled waveforms for each of these configurations (including voltage &

current harmonic content) may be observed over the following pages.

Event Details/Waveforms

13:00:24.8021/03/2011

13:00:24.85 13:00:24.90 13:00:24.95 13:00:25.00

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H02H03

H04H05

H06H07

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A VHarm A IHarm

T&R 100ADM - No Filter21/3/11

D Rothwell

CDG00

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Event Details/Waveforms

13:38:24.8021/03/2011

13:38:24.85 13:38:24.90 13:38:24.95 13:38:25.00

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H02H03

H04H05

H06H07

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A VHarm A IHarm

T&R 100ADM + Filter21/3/11

D Rothwell

CDG01

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Event Details/Waveforms

14:11:31.8021/03/2011

14:11:31.85 14:11:31.90 14:11:31.95 14:11:32.00

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H02H03

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Sverker 760 - No Filter21/3/11

D Rothwell

CDG02

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Event Details/Waveforms

14:35:58.8021/03/2011

14:35:58.85 14:35:58.90 14:35:58.95 14:35:59.00

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H04H05

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H12H13

H14H15

H16H17

H18H19

H20H21

H22H23

H24H25

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A VHarm A IHarm

Sverker 760 + Secondary Resistors (126.5 Ohm)21/3/11

D Rothwell

CDG03

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Event Details/Waveforms

08:34:17.8022/03/2011

08:34:17.85 08:34:17.90 08:34:17.95 08:34:18.00

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H02H03

H04H05

H06H07

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H12H13

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H18H19

H20H21

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A VHarm A IHarm

Sverker 760 + Tx 100Ohm Resistor21/3/11

D Rothwell

CDG04

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Event Details/Waveforms

08:40:51.8022/03/2011

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HG02HG03

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A VHarm A IHarm

Sverker 760 + Tx 100 Ohm R + Secondary R (126.5 Ohm)22/3/11

D Rothwell

CDG05

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Event Details/Waveforms

09:35:47.8022/03/2011

09:35:47.85 09:35:47.90 09:35:47.95 09:35:48.00

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Omicron 256 (280VA @ 7.5A / 40V rms Configuration)22/3/11

D Rothwell

CDG06

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Event Details/Waveforms

10:51:08.8022/03/2011

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H02H03

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H18H19

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A VHarm A IHarm

Sverker 760 + T&R AMD100 Filter22/3/11

D Rothwell

CDG07

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Event Details/Waveforms

13:39:09.7522/03/2011

13:39:09.80 13:39:09.85 13:39:09.90 13:39:09.95 13:39:10.00 13:39:10.04

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H02H03

H04H05

H06H07

H08H09

H10H11

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H16H17

H18H19

H20H21

H22H23

H24H25

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A VHarm A IHarm

Sverker 650 - No Filter22/3/11

D Rothwell

CDG08

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Event Details/Waveforms

14:10:35.8022/03/2011

14:10:35.85 14:10:35.90 14:10:35.95 14:10:36.00

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HG02HG03

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A VHarm A IHarm

Sverker 650 + T&R 100ADM Filter22/3/11

D Rothwell

CDG09

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Event Details/Waveforms

14:24:24.1022/03/2011

Tuesday

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A VHarm A IHarm

APTS - 3 Phase22/3/11

D Rothwell

CDG10

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Event Details/Waveforms

14:30:06.8022/03/2011

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H02H03

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H12H13

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H18H19

H20H21

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A VHarm A IHarm

APTS - 1 Phase Parallel22/3/11

D Rothwell

CDG11

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Event Details/Waveforms

14:33:27.8022/03/2011

14:33:27.85 14:33:27.90 14:33:27.95 14:33:28.00

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H02H03

H04H05

H06H07

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H10H11

H12H13

H14H15

H16H17

H18H19

H20H21

H22H23

H24

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A VHarm A IHarm

APTS - 1 Phase Series22/3/11

D Rothwell

CDG12

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Results Summary Table

Test No. Test Setup 2x Op Time (sec) Op Time Deviation %

Voltage HDF % (3rd Only)

Current HDF % (3rd Only)

00 T&R 100ADM – No Filter 14.78 47.4 4.74 82.22 01 T&R 100ADM + 100ADM Filter 10.35 3.2 113.84 17.39 02 Sverker 760 – No Filter 15.32 52.7 1.58 82.22 03 Sverker 760 + Secondary Resistors (126.5 OHM) 13.69 36.5 50.60 66.41 04 Sverker 760 + Primary Resistor (100 OHM) 15.27 52.2 6.32 82.22

05 Sverker 760 + Primary (100 OHM) + Secondary R (126.5 OHM) 13.44 34.0 66.41 53.76

06 Omicron 256 (280VA @7.5A 40V RMS Output / No Filter) 10.67 6.4 221.36 490.15

07 Sverker 760 + T&R 100ADM Filter 10.31 2.8 121.75 15.81 08 Sverker 650 – No Filter 15.28 52.3 1.58 86.96 09 Sverker 650 + T&R 100ADM Filter 10.50 4.7 117.00 12.65 10 APTS – 3 Phase (No Filter) 11.80 17.6 105.94 72.73 11 APTS – 1 Phase Parallel (No Filter) 15.08 50.3 53.76 74.31 12 APTS – 1 Phase Series (No Filter) 9.85 -­‐1.8 23.72 142.30

Conclusions The most significant relationship to note from these tests is that of operation time Vs. Current HDF. Generally speaking the greater the distortion of the test set current waveform, the greater the inaccuracy of the current driven relay timing will be. The Voltage HDF also has some impact, but it is marginal compared to the current waveform. The two exceptions to this general rule are the APTS and Omicron sets. Even with large waveform distortion factors, both of these test sets if selected to the appropriate output mode, were capable of providing accurate operation times on the CDG16 relay. Due to the severe distortion of the waveforms, there is either an ingenious software algorithm manipulating the output amplifiers in place, producing an accurate RMS sine waveform value, or both tests were a fluke. To determine accuracy of operational timing for these electronically controlled test sets, both should be examined separately at a variety of values (I.E. plotting the full IDMT curve). Utilising the primary and secondary resistors available to the Sverker range of test sets only marginally reduced harmonics & improved timing results on the CDG16 relay. It was noted however that these resistors did greatly increase the current resolution/sensitivity of the sets. We can unequivocally identify from these results is that all non-­‐electronically controlled test sets should be used with the addition of a filter such as the T&R 100ADM employed in these tests. All of the test sets coupled with the filter produced results within 5% of the ideal/theoretical timing value. Excluding the filter their timing deviations ranged from 34.0-­‐52.3%.

Future Investigation (-­‐ What? Test Set Issue 2) The conclusions of this report have been derived from the worst-­‐case secondary injection scenario using the CDG16 EF relay. Although this was a great starting point for investigating a range of test sets, test findings may prove more fruitful using EM relays of a lesser impedance. The next series of test aims to examine the functionality of the same test set configurations with a commonly placed 5A distribution EM IDMT relay. Following these tests, self-­‐powered protection relays such as the VIP300 shall be examined.

Appendices A-­‐ Data Sheet For 100ADM Filter

Features • Forces test current to a sinusoid

• Improves timing accuracy when testing electromechanical relays

• 0.25A-100A ranges

• High overload capability

• 50/60Hz operating frequency

• High efficiency

The 100ADM-F filter unit reduces the level of current harmonics when testing electro-mechanical protection relays. It is designed for use with our range of secondary injection test sets.

All electromechanical protection relays have iron cores that saturate and distort the test current under high overload test conditions. This distortion causes significant errors in the measured trip time of these relays during testing. Distortion of the waveform can be a particular problem with disc induction type over-current and sensitive earth fault relays.

For example, testing a CDG11 disc induction over-current relay without a filter causes significant timing errors. The results below show the errors for a 1.3s 1A CDG11 over-current relay on its 0.5A plug setting, tested at 5A.

Current THD Trip time Error

No Filter 5A 34.5% 1.54s 18.5%

With Filter 5A 6.12% 1.30s 0%

Current Filter Unit 100ADM-F

The 100ADM-F has nine current ranges covering 0.25A to 100A and is supplied in an insulated case complete with protective cover and carrying strap.

Resistor Box RB10

Current waveforms for disc induction relay

Unfiltered

Filtered

Features • Improves current control into low impedance

loads

• Particularly suitable for solid state relays

• 0.5Ω—1666.5Ω in 8 steps

• Maximum current 0.2—10A

• Thermal cutout

• Compact & lightweight

The RB10 resistor box is used in conjunction with a current injection unit when testing low impedance relays and trips, allowing finer control of the current. The unit is designed for use with the 100ADM and 200ADM, but may be used with any suitable current source.

The unit has eight resistance ranges with a maximum power dissipation of 50W for any one resistor.

Range Continuous Intermittent Maximum current current* voltage 0.5Ω 5A 10A 5V 1.5Ω 3.5A 7A 10V 6.5Ω 1.5A 3A 25V 16.5Ω 1A 2A 50V 66.5Ω 0.5A 1A 100V 166.5Ω 0.35A 0.7A 150V 666.5Ω 0.15A 0.3A 250V 1666.5Ω 0.1A 0.2A 250V *3 minutes on/8 minutes off The RB10 is supplied in a robust aluminium case, and all connections are made by industry standard 4mm safety sockets.

The RB10 has fuse and over-temperature protection.

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Note: Due to the company’s continuous research programme, the information above may change at any time without prior notificatio n. Please check that you have the most recent data on the product. T&R Test Equipment Ltd, 15-16 Woodbridge Meadows, Guildford, Surrey, GU1 1BJ, UK

Tel: +44 (0)1483 207428 Fax: +44 (0)1483 511229 email: [email protected]

www.trtest.com

Current Ranges and Ratings Range Continuous 5 min on/ rating 15 min off 0.25A 0.125A 0.25A 0.5A 0.25A 0.5A 1A 0.5A 1A 2.5A 1.25A 2.5A 5A 2.5A 5A 10A 5A 10A 25A 12.5A 25A 50A 25A 50A 100A 50A 100A

Frequency The unit may be used at either 50Hz or 60Hz, selectable by a switch on the front panel.

Range Selection The lower ranges (0.25A-50A) are selected by a switch, and the highest current range (100A) is selected by a terminal.

Current Monitor A current monitoring output is provided that gives an output of 0-100mA corresponding to the rated current for the range.

Filter Unit Impedance Range Impedance (Ω) 50Hz 150Hz 250Hz 350Hz 0.25A 880Ω 17.5kΩ 30.4kΩ 41.5kΩ 0.5A 220Ω 4.38kΩ 7.65kΩ 10.3kΩ 1A 47.7Ω 950Ω 1.65kΩ 2.25kΩ 2.5A 7.8Ω 150Ω 250Ω 360Ω 5A 1.94Ω 38Ω 65Ω 90Ω 10A 510mΩ 9.5Ω 16.5Ω 22.5Ω 25A 85mΩ 1.5Ω 2.5Ω 3.6Ω 50A 22mΩ 380mΩ 650mΩ 900mΩ 100A 5.5mΩ 95mΩ 165mΩ 225mΩ

Temperature Range Storage -20°C to 60°C Operating 0°C to 45°C

Dimensions Weight 340mm x 230mm x 330mm 15.6kg Accessories Current monitor plug and lead Optional Accessories 100AL lead set

100ADM-F RB10 Data Sheet Rev 1 19/9/05

Current Waveforms The waveforms below show the current and voltage for a disc induction type relay supplied from a 100ADM.

100ADM-F Specification

Disc induction relay without filter unit

Voltage

Current

Disc induction relay with filter unit

RB10 Specification Resistance Ranges and Ratings The RB10 has eight resistance ranges. Range Continuous Intermittent Maximum current current* voltage 0.5Ω 5A 10A 5V 1.5Ω 3.5A 7A 10V 6.5Ω 1.5A 3A 25V 16.5Ω 1A 2A 50V 66.5Ω 0.5A 1A 100V 166.5Ω 0.35A 0.7A 150V 666.5Ω 0.15A 0.3A 250V 1666.5Ω 0.1A 0.2A 250V *3 minutes on/8 minutes off Range Selection The appropriate range is selected by 4mm safety sockets on the front panel of the unit.

Temperature Range Storage -20°C to 60°C Operating 0°C to 45°C

Protection The unit has over-temperature protection and the common terminal is fused with a T10A fuse.

Dimensions 220mm x 163mm x 72mm including earth teminal

Optional Accessories S000-0534 5m low current lead set

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