insulation defect locator, idl-2x50-100 dual clamp...

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Insulation Defect Locator, IDL-2x50-100

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European Distributor: SenisGmbH; Technoparksrtrasse 1,8005 Zurich, Switzerland; www.senis.ch; tel +41 44 5087029Americas Distributor: GMW Associates: 955 Industrial Road, San Carlos, CA 94070, USA. www.gmw.com. +1 (650) 802-8292Revision Date: July 19, 2011

Dual Clamp-On Direct-Current MicroAmmeter Transducers for Insulation Leakage Current Localization Operating Principle

The Ametes Insulation Defect Locator (DFL) utilizes two high sensitivity clamp-on microam-meters to indirectly measure and track direct current passing through a defect or fault in the insulation system and determine the position of a leakage current path to ground. The DFL is capable of being used with the insulation system energized to high voltage. By indirectly measur-ing the leakage current, the defect or fault can be located without cutting conductors or removing insulation. This avoids the “divide-and-test” methodology, allowing the user to locate the defect quickly and significantly reduces repair time and effort.

This system has been designed for use with, but is not limited to, large hydo generator stator windings.

For example, with a 100Mohm resistive leakage path to ground, the leakage current, I, is 100µA when the applied potential is 10kV. CT1 measures 100µA and CT2 (which is just past the defect/fault) mea-sures zero. The capacitance from the windings to ground, shown as 0.5uF in this example, is initially charged by a current which is measured by CT1 and CT2. In the screen display corresponding to this example, the upper trace for CT1 shows the 100µA dc resistive current following the approximately 300µA peak capacitance charging current. The lower trace for CT2 shows the capacitive current, but no dc resistive leakage current.

HV

0.5uF

10 kV

CT1

CT2

100M I

I

Figure 1: Schematic for the Coil Array Test, Leakage Resistance “above” CT2

Figure 2: Example Print-Screen for Figure 1 Schematic

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System Description

The IDL System is controlled by a laptop PC with LabView software to control the High Voltage Power Supply output voltage and to acquire the instantaneous current outputs from the two MicroAmmeter Current Transducers. The software includes averaging of the current readings and presentation of the data with selection of the scaling for the current versus time display. To ensure that the capacitive charging current is maintained within the linear range of the current transducers, the software generates a smooth, selectable ramp profile for the High Voltage Bias Power Supply output voltage.

A fiber-optic USB link from the laptop USB port to the System Interface Cabinet provides electrical isola-tion and any desired cable length.

220/110V

100E

100E

USB via fiberoptics (Baaske)

DAQ module

HV supply

Ana

log

Out

2

USB

USB

ISO Amp+ Input module

Power module

100H

Power supply +12V, -12V,+5V

Ramp control

ISO AM

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In 1

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In 2

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Out

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Current TransducersSystem InterfaceControl Computer

Figure 3: Block Diagram of IDL System

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Cables up to 15m length from the System Interface (SI) to the Current Transducer 100E Amplifiers enable the interface to be located conveniently, even when the Current Transducers are moved to different locations in a large electrical system.

Normally the System Interface can be left in the Transit Case and near the High Voltage Bias Power Supply. All connections to the System Interface, including the 115V/230V ac power, are accessible from the front panel.

Short cables from the 100E Amplifiers to the 100H Current Transducer Heads enable the dimensions and weight of the head to be minimized to provide maximum flexibility in locating and orienting the 100H Heads in a complex winding geometry such as the generator stator shown. Figure 4: System Interface (SI) with Modules

Figure 5: Application on Electrical Generator Stator. The two 100H Current Transducer Heads are shown installed on the winding links.

Reprinted by permission from the US Department of the Interior, Bureau of Reclamation (USBR).

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IDL-2x50-100 System Features:

• Two clamp-on 50-100 Current Transducers to enable current difference measurements in electrical conductors at high voltage.

• Conductors do not have to be cut or insulation removed.• Simultaneous current measurements enable defect or fault location in complex systems, even with

more than one leakage path to ground.• Computer control via fiber-optic isolated USB interface for electrical isolation and operator safety.• High Voltage Bias Power Supply output ramp profile programmed from the computer to provide

reproducible, smooth voltage ramps to avoid high current capacitive charging transients.• Data acquired and displayed in real time for immediate analysis.

Specifications: 50-100 MicroAmmeter Current Transducer

50-100H Current Transducer Head

• Clamp-on Head Separable into Two Parts• Aperture Diameter: 51mm• Dimensions: 152mm x 96mm x 62mm• Weight: 0.6kg• Output Cable to Amplifier: 1m• Sensitivity to External Magnetic Field: <5mA/50µT• Voltage Isolation: ±5kV dc

50-100E Current Transducer Amplifier

• Sensitivity to Primary Current, SNOM: 100mV/mA• Tolerance of Sensitivity: < ±10% of SNOM

• Temperature Coefficient of Sensitivity: <±3%/°C• Equivalent Primary Current Noise: ±10µA• Frequency Response: dc to 1Hz (-3dB)• Maximum Output Signal: ±10V corresponding to

±100mA• Output Signal Source Resistance: < 100ohm, short

circuit proof• Dimensions: 230mm x 105mm x 67mm• Weight: 0.4kg• Output Cable to System Interface: 15m

Figure 6: Mechanical Drawing of a 50-100H Current Transducer Head

Figure 7: Assembling a 50-100H Current Transducer Head on a winding link

of an Electrical Generator Stator Reprinted by permission from the USBR.

insulation defect locator, idl-2x50-100 dual clamp...

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