Transformer and Switchgear High Voltage Testing
Does your high voltage system require extension or upgrade? Whether it be a transformer replacement or installing a new power station or substation, Megavar has the personnel, expertise, and equipment to perform all necessary protection and high voltage testing.
Do you have a high voltage testing and condition monitoring program for your high voltage assets? Have you considered what the direct and indirect costs may be, if a major electrical failure occurs in your HV system? If you answered no or do not know, then perhaps it is time to consider establishing high voltage testing and condition monitoring programs on your critical HV plant. Megavar can assist with the development and scoping of a suitable testing regime, as well as providing all high voltage testing and condition monitoring services.
FRA (Sweep Frequency Response Analysis)
Frequency response analysis is the world wide accepted standard test for detecting electrical and mechanical changes of the core and winding assembly of power transformers without costly de-tanking. It is common to perform this test in the factory and then again following delivery to site to determine and compare the transformer frequency response signature. Megavar engineers use the Omicron FRAnalyzer to provide accurate and detailed results for clients including Wilsons Transformers and ABB Transformers.
Dirana (Transformer, VT, CT and cable- FDS and PDC dielectric response analyser)
The DIRANA is an Omicron patented device that analyses the moisture content of the oil-paper-pressboard insulation medium. This is probably the most important ageing indicator for power transformers and an accurate knowledge of the moisture levels is vital knowledge for maintenance engineers who must determine whether dry out is required. Megavar offers engineers experienced in the operation of this device.
Dielectric Loss Angle Measurement (DLA, power factor, dissipation factor, DDF)
DLA of windings and bushing is common practice for the condition monitoring of current transformers, voltage transformers, power cables and power transformers. The measured values and the trend data from one test to the next will show degradation of the insulation and can be used in predictive assessment to determine the best time for costly maintenance. Megavar utilises the Omicron CPC+TD1 test system along with the omicron reactor to perform measurements to the highest accuracy.
Dynamic Contact Resistance Measurement
Dynamic resistance measurements is a novel technique developed to determine wear on the primary contacts of circuit breakers. It is probably most valuable for the condition monitoring of SF6 insulated switchgear, where the cost of inspections is great due to gas recovery and management during the inspection. The test set injects a current of up to 200A through the and measures the voltage developed during breaker operation while measures the travel curve through rotary and linear transducers. Megavar engineers are trained in the operation of the ISA CBA 2000 breaker analyser.
Circuit Breaker Contact Operating Time and Travel Analysis
The time that a circuit breaker takes to operate is of great importance, as it needs to be fast enough that it clears the fault rapidly and fits within the grading allowances for the protection scheme. Another factor that is not as widely known is the importance of the velocity of the contacts at the point that the primary contacts part as this determines how effectively the CB will break the current. To determine the velocity, acceleration and deceleration of the contacts through the stroke, a time/travel test needs to be performed. Megavar utilises the CBA 2000 unit for time travel testing on all timing parameters. For simple open, close and open-close-open timing sequence tests we can also use our Megger TM1600.
Transformer Standard Testing Regime
When commissioning new transformers and during routine condition monitoring it is common to test:
- winding resistance per tap
- ratio per tap
- vector group relationship
- leakage reactance
- excitation per tap
- tap changer continuity
Current Transformers and Voltage Transformers
The CT's and VT's in all substation provide vital current and voltage signals for protection and monitoring, which means it is important to verify that they meet the specification, are installed correctly and have their secondary circuit correctly wired. Megavar performs a range of tests (ratio, polarity, Kneepoint, winding resistance, burden) on CT's and VT's using the CPC100 multifunction test sets. Sometimes it is necessary to test CT's that have higher accuracies and kneepoints in excess of the capability of the CPC100, for these applications we have the Omicron CT Analzer with the CT SB2 automated switchbox. This allows us to test CT's with the greatest possible accuracy and efficiency for our clients.
Cable VLF Hipot (Very Low Frequency Hipot) and cable DLA
It is highly recommended and often mandatory to perform a VLF test on all HV cables following jointing or prolonged outages. This is done to prove the integrity of the cable prior to system energisation thus avoiding a high power failure of the cable when first connected to the system. Megavar engineers are experienced in using the HVI VLF-6022CM and the HV Diagnostics HVA60 units which we own. The advantage of the HVA 60 is that it can be used with our TD60 dielectric loss angle test set for assessing cable insulation and finding faults before the result in an insulation failure. link to HVA60 and TD 60 Brochures
IR and PI (insulation resistance and polarisation index)
One of the cornerstone tests for all primary substation equipment is the insulation resistance and polarisation index. These tests indicate the quality insulating quality of a dielectric by applying a DC voltage and measuring the current flow to present the insulation value in ohms and trend this value over a time interval of 10 minutes. Megavar uses high quality Megger units and is able to test to 10kV if required.
AC Power Frequency Hipot Testing
Most clients for whom we commission new HV assets, require that hipot testing of switchgear and busbar be performed prior to the initial system energisation. This is done to prove the integrity of the insulation at a voltage level higher than the system voltage, thus giving the confidence that the apparatus is well equipped to handle the system voltage. Megavar operates the ALT120/60 from HVI and the BK130 from Phenix. link to HVI ALT 120 and Phenix BK130 Brochures
