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VLF insulation testing

VLF testing uses very low frequencies as part of an AC cable maintenance routine. VLF testers are smaller and more practical than AC testers but output the same amount of power as a 50 Hz mains device. This combination of size and power makes Very Low Frequency cable testing perfect for testing longer sections of cable and apparatus.

AC is the standard used to transmit power worldwide, usually at a frequency of 50 or 60 Hertz. While supplies to railways and aircraft may use 162/3 of 400Hz, it is still a sinusoidal voltage waveform. A VLF test is ideal for working within these parameters.

Transmitting power with an alternating current is not as efficient as with a direct current however: while all power transmission lines and cable networks do have the side effect of DC resistance loss to the supply voltage, the level of capacitive loss is even higher. This is largely due to the inherent coupling between the phases involved. As a result, generating systems must supply enough energy to meet user demand as well as compensate for the large losses stemming from the transmission process. The small size and high power of the VLF tester helps to solve the practical problem of transmission loss during an AC test on very long sections of cable and apparatus in the field.

This equipment negates the need for on-site generation, large step down transformers or generating company supplies to be employed to power the items under test.

Because VLF testing supplies a working frequency of 0.1Hz as opposed to the 50/60Hz usually required for live transmission, the physical size of the VLF test set is massively reduced. Critically, the test object still receives the Alternating Sinusoidal Voltage that would be supplied through everyday use, but the size of the test equipment is much smaller.

VLF Sine Wave 34 kV - CABLE TESTER

  • High test capacity of 5 µF
  • Suitable for outdoor use (IP 54)
  • Single-button operation
  • Integrated safety system
  • Reporting
  • Continuous duty cycle
The VLF sine wave 34 kV is a compact, robust and portable VLF sine wave test system for medium voltage cables.

The design, optimized for rapid transportation and quick setup, and the continuous duty cycle are two attributes that qualify the system

as an ideal tool for routine cable testing. For both 0.1 Hz sine wave voltage tests and rectangular or DC voltage tests, the VLF sine wave 34 kV fills the highest demands on the test voltage quality and stability. Moreover, the integrated “breakdown detection“ shuts down the test voltage in the event of an excessive charge current and guarantees limited damage to the cable.

Consistent single-button operation combined with a sophisticated operating concept allows a fast and targeted use of the system.

VLF Sine Wave 45 kV - CABLE TESTER

  • Test capacity of up to 10μF – that’s up to 40 km or 25.8 miles of cable at reduced frequency and voltage
  • Internal tanδ option with automatic results interpretation
  • One minute burn after fault detection
  • Automatic frequency adjustment based on cable length
  • Adjustable DC pulse rates of 1:3 and 1:4
  • IEEE compliant withstand testing for new installations up to 25 kV
  • IEEE 400.2 compliant maintenance testing up to 35 kV
  • IEC 60229 compliant sheath testing up to 20 kV DC
The VLF Sine Wave 45, with optional integrated tanδ, is a compact system for commissioning, testing and condition analysis of medium-voltage cables. This unit performs very low frequency (VLF), DC, and sheath integrity testing as well as sheath fault pinpointing when combined with the optional ESG NT step voltage probe. Ideal for both routine testing and complicated diagnostics, the VLF45 has a multi-purpose design with a continuous duty cycle.

For 0.1 Hz sine wave, rectangular or DC voltage tests, the VLF45 provides enhanced voltage quality and stability. In the event of excessive charge current integrated breakdown detection shuts down the test, ensuring limited damage to the cable. Up to 1000 measurements can be stored in the internal memory and results can be viewed on the unit or downloaded via the USB port to the included Easyprot software for reporting.

An optional internal tanδ is available that automatically evaluates results for PE, XLPE and PILC type cables based on insulation and selected compliance standard. Combined with the optional ESG NT step voltage probe, the VLF45 can pinpoint sheath faults.

VLF Sine Wave 62 kV - TEST AND DIAGNOSTIC SYSTEM FOR THE TESTING AND CONDITION ANALYSIS OF MEDIUM VOLTAGE CABLES

  • Performs cable withstand testing, cable diagnosis and sheath fault pinpointing
  • Smallest and lightest unit on the market in its class
  • Automatic result interpretation as per latest IEEE 400.2 standard
  • Easy field operation with no need for external computer
The VLF Sine 62 kV, with integrated tan delta, is a compact, robust, and portable high-performance test and diagnostic system for medium voltage cables.

The VLF Sine 62 kV tester is a multifunctional tool. Not only can it perform VLF and DC testing, but it can also perform sheath testing and sheath fault pinpointing. Moreover, the optional internal tan delta expands the system to assess both cable integrity and condition. The smart VLF system automatically adjusts the test frequency to the cable length, making even tests on 35 kV rated cables (up to 25 km) easy and reliable.

VLF CR-28, VLF CR-40 and VLF CR-60 - COSINE RECTANGULAR CABLE TEST SYSTEMS

  • VLF, DC and sheath fault testing in one device
  • Portable thanks to two-part construction
  • High test capacitance
  • Integrated discharge system
  • Reporting
The portable, high-performance and energy-efficient VLF test systems are used for testing cables with 0.1 Hz cosine-rectangular voltage according to IEC/IEEE/CENELEC standards. In accordance with guidelines, the dielectric strength of cables and joints must be checked after installation or repair.

The VLF test systems from SebaKMT have high test-capacities and are still compact, because of the patented voltage wave-shape and the power-recycling during polarity reversal. Aside from cable and sheath testing, the test systems can also be used for the precise pinpointing of sheath faults (in combination with a step-voltage probe).

In total three portable systems are available, each with different voltage levels (28, 40 and 60 kVrms):
  • VLF CR-28 up to cable series 15 kV
  • VLF CR-40 up to cable series 23 kV
  • VLF CR-60 up to cable series 35 kV

VLF CR-60HP and VLF CR-80 - COSINE RECTANGULAR CABLE TEST SYSTEMS

  • Very high test power without frequency reduction
  • Covers cables up to 20 km at maximum voltage
  • No polarisation effects as with DC
  • Protocoling
  • Breakdown detection
  • Leakage current measurement
Powerful 0.1 Hz VLF test system with energy recovery for testing of cables with Cosine Rectangular Wave voltage according to VDE, IEC and IEEE.

In accordance with most regulations, cables and joints must be tested after installation or repair. The Seba KMT VLF Test System CR 60 kV can be used to test cables with operating voltage levels up to 36 kV. The system consists of a control unit and a HV unit. The high test capacity of 6.5 μF permits the simultaneous testing of all three phases. Positive and negative DC testing of cables and connected switchgear can be carried by DC Mode.

This VLF Test System CR 60 kV can be used both as a stand alone system and as integrated part of a test van system.

Tan delta attachment - VLF SINE SYSTEM ACCESSORY

  • Very accurate measurement
  • Optional leakage current correction
  • High wireless range
  • Measurement at high voltage potential
The tan delta test attachment enables a precise determination of the condition of the cable. Integral aging effects, such as the degree of humidity and “water treeing” can be simply recognized and quantified, making the tan delta test attachment the ideal instrument for monitoring the condition of the cable.

The tan delta test attachment can be used as a stand-alone system with the portable VLF sine systems or in combination with the integrated VLF sine test systems in vehicles.

The system achieves very accurate measurements because it measures at the high voltage potential and the measuring head can be placed very close to the test object.

EasyTest 20 kV - VLF AND DC 20 KV CABLE TEST SYSTEM

  • Easy to operate
  • Configurable test sequences
  • AC, DC and sheath testing in one single system
  • Reporting via USB or Winkis
The Easytest represents a simplified version of the standard VLF test. It has been designed to verify operational integrity versus operational reliability, which is the objective of a standard VLF test in accordance with the respective standards.

Typically, a simplified test is performed in accordance with company specifications after repairs or after a new cable or circuit has been installed. The purpose of such a test is to verify the integrity of the cable and there accessories before switching the circuit back into operation. The Easytest allows such a test at voltages well above operating voltage in order to provide a safe indication regarding operational integrit
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