Industrial Project Seminar on : Industrial Project Seminar on EHV Testing of Power Products &
Power Factor Improvement
Industry: Prepared By:
ABB Ltd. Kandarp Mistry
Sujan Singh Thakur Aggenda : Aggenda Overview
High Voltage Power Products
High Voltage Testing
Problems and Solutions
Power Factor Fundamentals
Improve Power Factor
Benefits Overview : Overview ABB India’s Corporate R&D Lab at Vadodara gets stamp of recognition from National Accreditation Board For Testing and Calibration Laboratories (NABL).
India’s testing division of the R&D Lab was given the NABL recognition for its compliance to ISO/IEC 17025 standards in the testing process. The EHV and Insulation laboratory are also included in the scope of accreditation.
High Voltage Power Products
(1) Power Transformers
(2) Instrument Transformers
(4) Isolators and Circuit Breakers
(6) Surge Arrestors High Voltage testing : High Voltage testing The high voltage test (also called dielectric strength test or hipot test) can be made in AC or DC. If the high voltage test is made in DC, it is then combined with insulation ; if the high voltage test is made in AC, it is then, this is then, more stressful for the sample and made according to the sketch below.
Measurement of high voltage test under alternating current is performed using an alternating voltage (50Hz) adjustable to an effective 50V to 1,500V. As is the case with direct current, the high voltage test detects any sudden rise of current up to a programmed threshold.
The short circuit test is maintained by default. The rise time is more than 500 ms and the application time at least one period.
Warning: The high voltage test under alternating current is penalised by the capacitive value of the tested equipment. It must be remembered that the generator power is limited to 5 mA. High Voltage testing : High Voltage testing Impulse Flashover test Dry
Switching Impulse Flashover test Dry & Wet
Power frequency Flashover test Dry & Wet
Voltage Distribution test
Corona Inception & Extinction test Slide 6: Power Transformer Small Power Transformer
In response to changing market needs, ABB has redefined its transformer product families and implemented a new buisness model around small Power Transformers, from 5 to 63 MVA and up to 170 kV. (3-phase with/without OLTC) Distribution Transformer : Distribution Transformer ABB Distribution Transformers (45 to 3000 KVA) are uniquely qualified to meet the needs of the utility, Industrial & Construction, and Energy Industries. Its quality DT is backed by a series of transformer tests used to verify conformance to performance characteristics outlined in the latest revisions of IEEE C57.12.90. These identified tests are also part of Quality System which is audited semi-annually by DET NOSKE VERITAS (DNV) to the ISO standards. Transformer Testing : Transformer Testing Induced Over Voltage Test
Transformers are tested for over voltages by exciting the secondary of the transformer from a high frequency a.c. source (100 to 400 Hz) to about twice rated voltage. This reduces the core saturation and also limits the charging current necessary in large power transformers. The insulation withstand strength can also be checked.
Partial Discharge Test
Partial Discharge tests on the windings are done to assess the discharge magnitudes and the radio interference levels. The transformer is connected in a manner similar to any other equipment and the discharge measurements are made. A high percentage of medium and high voltage equipment failures occur due to partial discharges (PD). Partial discharges are partial failures of the insulation. These partial failures create minute sparking or arcing activities across the surface or within the bulk of the insulation. This micro-sparking produces signals in the radio frequency spectrum that are sampled, measured and analyzed using high frequency instruments and custom software. Once partial discharge activity occurs, insulation failure is imminent. Partial discharges generally occur at voids, cracks or other flaws where the localized electrical stresses exceed the capacity of the insulation. Slide 9: Impulse Testing The purpose of the impulse test is to determine the ability of the insulation of the transformers to withstand the transient voltages due to lighting, etc. Since the transients are impulses of short rise time, the voltage distribution along the transformer winding will not be uniform.
Advanced impulse test systems are used for carrying out impulse voltage tests on HV apparatus like Power Transformers, Instrument Transformers, Switchgear, Breaker, HV Cable etc.The tests are conducted with lightning (LI), full or chopped waves, and / or switching impulses (SI) as prescribed in the relevant international standards.Haefely impulse test generators all integrate several safety systems, which ensure a safe operation for personnel and test object.With the patented Overshoot compensation circuits (blocking of resonating effects between generator and test object) the impulse overshoot can be minimised respectively suppressed. Therefore overvoltages on highly capacitive test objects are avoided.
Impulse voltage generator – 1200 kV, 60 kJ and 800 kV, 40 kJ
250 mm sphere gap for HV measurement
Impulse voltage divider (damped capacitive type) – 1200 kv, 800 kV & 300 kV.
Multiple chopping gap of 1200 kV time control from 2-6 micro-seconds and rod gap arrangement
Double beam high-speed impulse oscilloscope with photographic attachment
10 bit digital impulse oscilloscope with software.
Low resistance non-inductance current shunt.
600 kV ac HV testing transformer
RIV Measuring Instrument. Guidelines for Using Voltage to Detect Insulation Defects : Guidelines for Using Voltage to Detect Insulation Defects Here are some guidelines for using voltage to find insulation problems in a cable or harness. Test Situation Recommendation:-
When air gaps between conductors can be less than 0.1” : - High-voltage breakdown testing is appropriate when air gaps of less than 0.1 inches can occur between conductors; . The testing often needs to be done above 500 volts to really be helpful.
Voltage must be more than 50 volts to be useful Testing at less than 50 volts can detect leakage or contamination but the low test voltage generally does not detect common insulation breakdown between conductors.
Test at voltages above the rated working voltage.: - Brief high-voltage testing at three times the rated voltage of cable assemblies and wire harnesses has not been known to damage or degrade insulation. A common aerospace guideline is to test at two times the operating voltage plus 1000 volts.
Insulation resistance testing: - Testing High-voltage Insulation Resistance (IR) is often needed when the cabling is used for sensitive low-power signals.
AC testing: High-voltage AC tests for large assemblies can create a shock hazard. For this reason, and also because of slower test speed and higher cost, it is not as popular as DC testing. In some circumstances, AC testing detects problems not found with DC tests, particularly when used with long application times. AC tests are known to degrade PVC insulation. When using a DC test to replace an AC test, raise the voltage by at least 40 percent.
Shock hazard: - High-voltage DC tests of cables shorter than 500 ft. do not need to be a shock hazard. A tester designed to test larger assemblies at higher currents can still be a hazard with wrong settings or if it malfunctions. IEC479-1 and EN61010-1:1993 specify a non-hazardous energy source as being less than 45 micro coulombs (this is 45 / 1500 = .03 micro-farads at 1500 VDC). This limit includes energy from both the tester and the assembly under test.
Which wires require testing: - Test voltages must be applied between all relevant combinations of wires, including shields, to test insulation. Slide 17: Voltage Ramp Rate in DC testing : Controlling the voltage ramp rate is a common way to limit the current needed to bring each wire up to the hipot voltage. A modern hipot tester can limit the inrush current and detect failures as the voltage is rising which makes the ramp rate specification unnecessary.
Burning out shorts and arcing: A high-voltage test that allows high currents causing visible arcing that burns out a short and then passes the wired assembly as good, cannot be relied upon for defect removal because carbon tracks and potential insulation damage may occur.
Voltage accuracy: Voltage accuracy must be within 10 percent or a higher voltage setting must be used that assures testing to within 10 percent of the specified test voltage.
Finding stray strands: High-voltage testing, unless done at many thousands of volts, does not detect stray strands unless they are within .050 of an inch of another conductor/contact. Partial Discharge Measuring Technology : Partial Discharge Measuring Technology The Partial Discharge Measuring Systems of ABB Ltd. are suitable for measurements of high voltage equipment, such as:
Motors and generators
Transformers and converters
Medium and High Voltage Cables
Capacitors Partial Discharge Measuring System : Partial Discharge Measuring System Complete Partial Discharge Measuring System LDS-6 with Measuring Impedance, Multiplexer and Calibrator Partial Discharge Measuring System : Partial Discharge Measuring System The Digital Partial Discharge Measuring System LDS-6 has the following main features:
Useable with standard PD measuring circuit according
Using advanced digital signal processing hardware
Different processing units (PU) available, like
wide band PU linear and logarithmic, narrow band PU.
Noise gating unit for sensor-controlled rejection of
external noise pulses.
Windowing unit for rejection of phase-related noise pulses Partial Discharge Measuring System : Partial Discharge Measuring System Differential LEMKE PROBE LDP-5 for on-site and laboratory
PD diagnosis tests
Using of capacitive or inductive field coupling mode Partial Discharge Technology : Partial Discharge Technology Ultrasonic PD Sensor for detection of partial
discharges by using acoustic emission
Location of external and internal PD sources
by different ultrasonic receivers
UHF/VHF-Converter for on-site PD detection
on power cable accessories under life condition Slide 24: PD Warning Device LDWD-6
for Continuous PD Monitoring of High Voltage Systems PD measurement : PD measurement PD measurement gives information about the condition of insulation i.e. quality of impregnation, presence of voids, cavities etc, which may cause deterioration of imitation over a long period.
Tank should clean to remove traces of oil & dust.
PD checks after HV testing done also…
Proper corona ring to cover cooler film. Slide 26: Tests done in Current Transformer
High Voltage Power Frequency test
Partial Discharge Measurement
Capacitor & Loss factor Measurement (tan ?)
Composite error Test
C ore Ratio Test
Knee Point Voltage Test
HV PF Test on secondary wdg.
Thermal Stability Test
Temp. Rise Test
Lightning Impulse Test
Visible Corona Test Capacitance and Loss Factor Measuring Technology : Capacitance and Loss Factor Measuring Technology (66 KV CT TESTING) : (66 KV CT TESTING) While testing 66kv we have to change the registor of lighting impulse generator. For testing of CT we are making the secondary of CT which is in terminal box, short circuited, because there is one turn in primary & multiturns in secondary. So when we apply High Voltage, as the ratio of primary to secondary is 1/no. of turns i.e. more the voltage produced at secondary & the equipment gets damaged plus chances for failure of person.
Ø So we are providing short circuiting through copper wire to the CT.
The foil type ground foil is used for impulse test while the single cable is used as ground cable for HV Test.
Ø If we use (orange type) cable then there is inductance produced. Because cores are there. But if we use foil then only one core i.e way to flow the current. As area large so resistance decreases & ground return better.
We are using inductive type resistors in impulse generator. Generally in impulse type, inductive coils are used but those stores energy. So we will get waveform (2).
Ø To get smooth waveform (1) we are providing the same turns, same material, and same wire but overlap it in opposite direction. Thus that is now purely resistor & no quantity of inductor is there now. Slide 29: For CT we are keeping full i.e. 3 units in series HV reactor. For HV testing, while for testing CVT, we short the bottom two units.
In CVT the capacitance is high as it is the capacitor voltage transformer. Thus according to Xc = 1/2?fc If C increases then Xc decreases. Now this HV generator has the series resonance principle i.e. X? = Xc. So, the balance the X? with Xc we are short circuit the bottom two units & providing only the 333 KV of 1st unit.
Why corona ring is providing for High voltage equipment testing?
To minimize the external discharges & to calculate only the internal discharges of the test object, the corona ring is provided.
If humidity in atmosphere is more than 80% then we should not do the tests.
Humidity in air is more than 80% then there are water particles on the surface of the insulators as shown. That water particles makes the conductivity path by expansion & there may be chances to breakdown or flashover. C & tand (power factor) measurement : C & tand (power factor) measurement Under the Tettex Instruments label we offer a broad range of precision C & tand measuring bridges covering both high and low voltage applications for laboratory, factory, workshop and field use.
Conditions of Test Pass
The test object shall be considered passed if
Dielectric loss factor is in the range of 0.2 to 0.3%.
Loss factor does not vary by more than 0.05 at different voltages.
Capacitance is within the limits mentioned in the test instructions.
If the test is done post any HV Test; the capacitance should not vary by a value equal to that of one grading than the value before HV Test.
e.g. For a CT with capacitance of 1000 pf & so grading by increase in capacitance due to failure of one grading would be 1000/80 = 12.5 pf. Slide 31: The DSP-based Dissipation Factor and
Capacitance Measuring System LDV-5 is suitable for high precision measurements of: Dissipation factor (tan d) Capacitance CX Test voltage Frequency Test specimen currents Power factor Main features of the LDV-5 are: : Main features of the LDV-5 are: Using advanced digital signal
processing (DSP) hardware
Using fully automatic measuring
procedure in the frequency range
between 10 and 400 Hz
Using integrated PC for
data storage andfile transfer
Individual setup possibilities Slide 33: The test cells can be used together with DSP-based Dissipation Factor and Capacitance Measuring System LDV-5 or Dielectric Analyzer DIANA for measurements of liquid and solid dielectric materials. Needs and Solutions : Needs and Solutions Power Factor Fundamentals : Power Factor Fundamentals Most Industrial loads require both Real power and Reactive power to produce useful work
You pay for BOTH types of power
Capacitors can supply the REACTIVE power thus utility doesn't need to.
Capacitors save you money!
Reduces Power Bills
Reduces I^R losses in conductors
Reduces loading on transformers
Improve voltage drop What is PF? : What is PF? INTRODUCTION
Most plant loads are Inductive and require a magnetic field to operate:
> Florescent Lighting
The magnetic field is necessary, but produces no useful work
The utility must supply the power to produces the magnetic field and the power to produce the useful work: You pay for all of it!
These two types of current are the ACTIVE and REACTIVE components The Power Triangle : The Power Triangle Power Factor is the ratio of Active Power to Total power: Active Power (kW) Reactive
Power Total Power (KVA) Power Factor = Active (Real) Power Total Power = KW KVA = cosine (a) What causes low power factor : What causes low power factor Inductive loads constitute a major portion of the power consumed in industrial complexes.
Reactive power (KVAR) required by inductive loads increases the amount of apparent power (KVA) in your distribution system. This increase in reactive and apparent power results in a large angle ¢. Recall that, as ¢ increases, cosine ¢ (or power factor) decreases. ¢ KVA KW KVAR ¢ KVA KW KVAR So, inductive loads (with large KVAR) result in low power factor Improvement of power factor : Improvement of power factor Installing capacitors (KVAR generators)
Minimizing operation of idling lightly loaded motors
Avoiding operation of equipment above its rated voltage
Replacing standard motors as they burn out with energy efficiency motors
Released System Capacity: Decreasing size of conductors required to carry the same 100kW load at p.f. ramging from 70% to 100%.
Reduce power losses