Current Transformer Burden Ammeter

Current Transformer Burden Ammeter is a rugged, portable instrument, designed to field-test current transformer installations for:

_ short-circuited secondary turns

_ short-circuited primary turns

_ short-circuited secondary wiring

_ high-resistance connections in the secondary circuit

_ grounding of secondary winding when mounted on a grounded structure

_ grounding of a normally ungrounded wire

APPLICATIONS

Within the accuracy limits of the CT, a good current transformer should not have a noticeable change in ratio when a secondary burden is added. This is because the primary effect of additional burden on a good CT is a rise in the secondary voltage.

However, if one or more turns of a CT are shorted, a substantial amount of the total available ampere-turns is diverted into the shunt path created by the short. Thus, the current to the circuit connected to the CT is less than

the CT’s total secondary current.

Therefore, when the proper burden within the ammeter is added in series with the circuit connected to a good CT, the current indicated by the ammeter should only decrease a few percent.

However, in a bad CT, the additional burden will cause even more current to be diverted into the shorted turn(s). This will cause the current indicated on the ammeter to decrease significantly. This sudden and large decrease in the ammeter reading will be seen immediately whenever the burden is added by using the switch.

FEATURES AND BENEFITS

_ Multi range ammeter incorporating switch-selected burdens

_ The burdens are normally shorted out, but can be put in series with the ammeter by a spring-loaded momentary switch

_ Designed to ensure that the secondary of the CT under test will not be accidentally opened; make-before-break construction used for ammeter range and burden selector switches

_ The instrument is housed in a rugged, moulded-plastic case. All leads extend away from the user to prevent contact with live components.

Arc Reflection Filters

Arc Reflection Filters marry impulse generators to high voltage “radars” (time domain reflectometers, TDR), providing fault locating crews with integrated systems to meet all cable fault locating needs. Two models are available:

_ Standard Arc Reflection Filter (detachable):

designed to withstand 1,000,000 Joules/hour (continuous operation with a standard impulse generator) and 50 kV proof/burn voltage.

_ Heavy-Duty Arc Reflection Filter (detachable):

designed to withstand over 3,000,000 Joules/hour (continuous operation with a heavy-duty impulse generator) and 70 kV proof/burn voltage. Choice of an Arc Reflection Filter is dependent upon the energy producible by the impulse generator with which it will be used. The Standard Arc Reflection Filter can be used with any non-heavy-duty impulse generator. The Heavy-Duty Arc Reflection Filter is used whenever the system includes a heavy-duty style impulse generator (generates in excess of 1,000,000 Joules/hour and/or 70-kV proof/burn voltage).  The arc reflection filter, including its sturdy metal cabinet of welded construction and all its components are designed to withstand the rough handling it will experience in the field. For operator convenience, a mode selector switch is provided on the top control panel. When the selector switch is set to ARC REFLECTION TEST, the arc reflection filter network is connected to the cable under test. This makes it possible for the operator to make either TDR tests or arc reflection tests, as well as other tests requiring the use of the filter. When the selector switch is set to the PROOF/BURN/ IMPULSE mode, the filter is bypassed, allowing stand-alone operation of the impulse generator system on impulse, proof or burn. A wide-band current transformer is permanently connected electrically and mounted inside the cabinet for use with the surge pulse.

APPLICATIONS

With Arc Reflection Filters, cable faults can be located on power cables rated at up to 35 kV. Relatively small systems, such as most direct buried underground residential distribution (URD) systems, are easily satisfied with the standard filter. Larger systems, including especially long direct buried distribution cable and especially complex circuits using lead-covered cable, require much more energy (such as is made possible using the heavy-duty filter).

FEATURES AND BENEFITS

Designed to withstand continuous operation

_System is not vulnerable to operator error (if left on after fault localization).

_System can be operated for the time required to localize complex faults.

_Operator can use the full proof-burn capability of the thumper in use.

Components designed as distributed circuit elements

_ Helps to provide a clear, distinct display on the companion TDR.

_ Helps to eliminate unwanted background reflections on the companion TDR by contributing less than 5% noise.

Slow voltage rise time

_ Limits the voltage that reaches the cable under test to the voltage required to break down the fault.

_ Operator cannot overstress a faulted cable while in the arc reflection mode.

Low output impedance

_ More effective in energizing large cable/network systems.

_ Improved fault locating capability.

High output current capability

_ Ionizes faults immersed in oil or water

_ Power matches the fault for more effective fault locating

Cable Route Tracer

The AccuTrace Cable Route Tracer consists of a transmitter, which energizes the line with a traceable signal, and a portable receiver, which detects the signal. The transmitter can energize the line either by magnetic induction from a built-in antenna or by direct conductive connection to the Metallic line. Energizing the line conductively provides increased tracing distance and minimizes signal coupling to other lines. Inductive coupling, which does not require a mechanical connection to the line, permits a buried line to be traced without uncovering or de-energizing it. The transmitter provides a simple, LO/HI pushbutton to adjust the transmitted signal’s strength, and a PULSE button for battery conservation and easy identification of the signal. The receiver can be used to trace lines using either peaks (detection of the maximum signal) or nulls (detection of the minimum, or zero, signal). The antenna is swivel-mounted for operation in vertical, horizontal or 45° mode used to calculate depth. The receiver provides audible and visual indication of detected signal strength. Simple controls adjust sensitivity and amplification, and a jack provides for audio output to an optional headset. Standard AA batteries provide up to 30 hours of continuous operation. When the receiver is not in use, the telescoping handle retracts for convenient, compact storage.

APPLICATIONS

AccuTrace locates and traces any conductive line such as cable, pipe or metallic conduit. Depth of the line can be established quickly by taking advantage of the swivel mounted antenna. Adding an optional ring clamp to the system provides a stronger inductive signal for tracing in areas with heavy cable activity. Blockages in water pipes such as sewer lines can be found with the use of an optional watertight capsule transmitter. A tape-on

Transmitter lets the operator locate collapsed duct work.

FEATURES AND BENEFITS

_ Easy to use and simple to operate, this cable route tracer can be used successfully the first day in the field.

_ Conductive coupling lets the operator discriminate between multiple utility cables in a common trench and trace the line of interest. Conductive tracing also increases tracing distance.

_ Inductive coupling lets the signal be transmitted without a direct metal-to-metal connection. The operator can trace an energized cable using a distinctive transmitted signal. Also, cables that do not have exposed terminations can be traced with ease.

_ Both peak- and null-tracing mode methods can be used during a single trace to ensure accuracy and speed. Null tracing is very fast and can be used to identify sharp direction changes. Peak tracing can be used to find the cable at the start of the trace and to identify cable location when conditions make null tracing ineffective. Super inductive circuitry allows, in the inductive tracing mode, the AccuTrace to trace longer lengths than any known competitor. If conditions such as cable depth make normal inductive tracing inefficient, the superinductor will produce a signal that the receiver can trace.

_ The receiver picks up only the distinctive transmitted signal by filtering out electric noise and static.

_ Extremely loud, adjustable audio output eliminates the need for headphones in noisy areas. This makes the AccuTrace more comfortable and easier to use than units requiring headphones and visual interpretation.

_ Extremely lightweight receiver increases operator comfort when tracing long cables or when using for extended periods.

Cable Phasing Meter

Cable Phasing Meter offers a safe and quick method of measuring voltage and determining phase rotation of underground distribution systems using the capacitance test point of elbow connectors. Most manufacturers of high-voltage cable terminators incorporate capacitance test points into their elbow connectors. These test points are designed for measuring purposes.

APPLICATIONS

The Cable Phasing Meter is an instrument designed to measure voltage, determine phase potation and phase out cables when connected to the capacitive test points. This instrument is battery operated and is supplied with a ground and two measuring leads.

FEATURES AND BENEFITS

_ Safe - operates at low voltage

_ Measures system voltage

_ Measures capacitance of test point if system voltage is known

_ Checks phase rotation of cables

_ Phases out cables

_ Rugged; comes with portable case

_ Battery operated

_ Operates from potential test point of elbow connectors

AC Dielectric Test Sets

The 50/100 kV AC Dielectric Test Sets are ac high-voltage sources for testing electrical insulation. The standard system includes a control/instrument cabinet, a high-voltage transformer assembly and all necessary cables including ground and input power.

The high-voltage transformer is installed in an oil-filled, heavy-duty, fibreglass tank permanently mounted on a cart with casters. Convenient points are provided on the tank top (0 to 100 kV) and side (0 to 50 kV) for connection to the high-voltage output. A voltage divider is permanently connected to the output terminals and installed inside the high-voltage tank for mechanical protection. A wing nut is provided on the cart for the ground connections. Storage space is provided on the cart for the control cabinet, instruction manual and cables.

                                                 

APPLICATIONS

These test sets consist of general-purpose ac high-voltage sources suitable for dielectric withstand (high-potential) testing of all types of electrical insulation. They also permit guarded leakage current measurements and are suitable for use with capacitance and dissipation factor bridge systems to measure insulation power factor.

The Megger 681100 Series test sets are recommended for testing capacitive loads that fall under the capability curve. Most electrical insulation systems are principally capacitive. Operation from 50-Hertz input supply permits a 20% increase in maximum load capability.

The Megger 686100 Series test sets are recommended for special applications involving resistive loads, or small capacitive loads with extended test durations.

FEATURES AND BENEFITS

_ Suitable for testing aerial bucket trucks according to ANSI A92.2

_ 50-kV tap with doubled output current permits testing bucket liners according to ANSI A92.2

_ Built-in, four-range output current meter with guard circuit

_ Four-range output kilovoltmeter has accuracy unaffected by sample loading

_ High-speed overvoltage and over current trip-out holds test voltage reading at instant of trip-out

_ Output signals are provided for both voltage and current meters, on all ranges, to permit external recording of test data

_ Zero-start safety interlock system with provision for external safety interlocks and warning lights

_ 15-ft (4.6-m) inter-unit cables, separate control and high voltage units for safety during tests

DC Dielectric Test Sets

Dielectric test sets measure leakage current while applying a dc voltage at or above the insulation system’s operating level. This measurement aids in determining the insulation system’s ability to withstand over voltages such as lightning strikes and switching surges.

APPLICATIONS

Portable DC dielectric test sets check the electrical insulation quality of motors, power cables, switchgear, insulators, transformers and capacitors. Typical applications include acceptance and maintenance testing of critical equipment used by electrical utility substations and industrial plant distribution systems. Power apparatus manufacturers may also use the equipment to perform QA/QC production tests. The test sets can be used to perform step-voltage and proof tests which, when incorporated into a routine maintenance program, can aid in predicting potential failure before breakdown occurs.

Two models are available; a 5-kV unit for testing equipment rated 2.5 kV and below, and a 15-kV model for use on equipment rated 7.5 kV and below. Both are suitable for testing power cable, switchgear and rotating machinery in accordance with IEEE, ICEA, NEMA and ANSI guidelines.

Megger DC dielectric test sets act like full-wave rectified units, they also are suitable for applications involving vacuum bottles.

DC vs AC High-Potential Testing

Direct current high-potential testing provides several advantages over alternating current. Direct current test equipment uses far less power, provides fast charging of highly capacitive test samples, can be easily transported to the test site and costs less. Additionally, the dc test can detect incipient breakdown without the possibility of damage to good insulation.

FEATURES AND BENEFITS

_ Compact and portable

_ Air insulated, uses no oil

_ ±2% accuracy

_ Leakage current measurement as low as 0.1 mA

_ Continuously variable test voltage with zero-start safety interlock

_ Fast charging of high-capacitance samples

_ Current guard circuit for highly accurate measurements

_ Strip chart recorder for hard copies (optionally available)

Safety and Reliability

_ Input and output line circuit breaker

_ Output current overload relay

_ Zero-start interlock for high-voltage output

_ Pushbutton controls and indicating lights for high voltage ON/OFF

_ Full circuit breaker protection

_ Connection for external permissive and safety interlocks

Safety in use of Electrical testing equipments (rated voltages less than 650V) .......7

Note: Special precautions and provisions may be necessary for current measurement in CT secondary circuits and such measurement techniques are outside the scope of the guidance in this document.

Where current measurements are to be made using instruments other than insulated tong-test type instruments, the connections should be made with the apparatus dead, and should be made secure before the power is switched on. Any such temporary connections need to be adequately rated both for current and voltage.

If regular testing needs to be done, for example on complex control panels, nearby bare live conductors should not be accessible (eg screened) where access is not required. Alternatively, purpose-made screened test points or instrumentation may be provided.

Examination of equipment

All items of test equipment, including those items issued on a personal basis, should receive a regular inspection and, where necessary, a test by a competent person. Records are recommended to be kept of inspection and testing of the equipment, particularly where faults are found. These records will help decide how often visual inspection or testing will need to be carried out. It is important that electricians are aware of the kinds of defect which may occur in test equipment. Examples of common faults are:

(a) Cracked meter cases;

(b) Damaged insulation (abrasion, cuts or perishing of flexible insulation);

(c) Loose terminals.

Safety in use of Electrical testing equipments (rated voltages less than 650V) .......6

Precautions during testing

For voltage detection or measurement, test leads protected by a fuse (or fuses) are recommended when voltmeters and in particular multimeters, are used. Although some multimeters are fitted with electromechanical overload devices, these are often inadequately rated to deal with short circuit energy present on electrical power systems. It is usually necessary to use leads which incorporate high breaking capacity (hbc) fuses even if the multimeter has an overload trip. If terminal clips are provided for connection to test points, they should be adequately insulated and arranged to be suitable for use with the test leads, as a safe alternative to the use of test probes. It is important that a multifunction or multirange meter is set to the correct function and/or range before the connections are made. Where there is doubt about the value of voltage to be detected or measured, the highest range should be selected at first, provided that the maximum voltage possible is known to fall within the range of the instrument.

Progressive voltage detection or measurement is often used to prove circuit continuity. The dangers from exposed live conductors should be borne in mind when using this method. In many cases, continuity testing can be carried out safely with the apparatus dead, using a self-contained low voltage dc source and indicator.

If tong-test instruments are to be used, it is necessary to check first that there is adequate working space free from danger (ie from bare live conductors at dangerous voltages) at the place where the instrument will be held. The tong insulation should always be examined visually before the instrument is used; if defects are present the instrument should not be used. 

Safety in use of Electrical testing equipments (rated voltages less than 650V) .......5

Precautions before testing

Before testing begins it is essential to establish that the test device including all leads, probes and connectors is suitably rated for the voltages and currents which may be present on the system under test.

Before any testing is carried out ensure that:

(a) The equipment which is to be worked on is safe for the intended tests; and

(b) The working environment does not present additional dangers. These dangers include:

(i) Inadequate space to work safely;

(ii) An insecure footing;

(iii) Insufficient light;

(iv) Potentially flammable gases or vapours;

(v) Explosive or conductive dusts.

Where a test is being made simply to establish the presence or absence of voltage, the preferred method is to use a proprietary test lamp or 2-pole voltage detector suitable for the working voltage of the system rather than a multimeter. Accident history has shown that the use of incorrectly set multimeters or makeshift devices for voltage detection has often caused accidents.

Note: Test lamps and some voltage indicators may fail to danger, eg. a faulty lamp not indicating a live circuit. These devices should be proved before and after use on a known live source of similar voltage to the circuit under test, or alternatively on a portable test source.

Safety in use of Electrical testing equipments (rated voltages less than 650V) .......4

Test lamps and voltage indicators are recommended to be clearly marked with:

(a) The maximum voltage which may be tested by the device; and

(b) Any short time rating for the device if applicable. This rating is the recommended maximum current which should pass through the device for a few seconds. These devices are generally not designed to be connected for more than a few seconds.

The use of test equipment by electricians falls into three main categories:

(i)     Testing for voltage (voltage detection);

(ii)    Measuring voltages; and

(iii) Measuring current, resistance and (occasionally) inductance and capacitance.

Item (a) forms an essential part of the procedure for proving a system dead before starting work but may also be associated with simple tests to prove the presence of voltage. Items (b) and (c) are more concerned with commissioning procedures and fault finding. 

Safety in use of Electrical testing equipments (rated voltages less than 650V) .......3

Sockets and terminals

Risks of inadvertent hand or finger contact with any live test socket conductor when the equipment is live need to be reduced. The terminals and test sockets of test equipment may require shrouding.

Voltage detection instruments

               Instruments used solely for detecting voltage fall into two categories. These are:

(i) Detectors which rely on an illuminated bulb (test lamp) or a meter scale (test meter). Test lamps fitted with glass bulbs should not give rise to danger if the bulb is broken. It may be protected by a guard.  These detectors require protection against excess current. This may be provided by a suitable high breaking capacity (hbc or hrc) fuse or fuses, with a low current rating (usually not exceeding 500 mA), or by means of a current-limiting resistor and a fuse. These protective devices are housed in the probes themselves. The test lead or leads are held captive and sealed into the body of the voltage detector.

(ii) Detectors which use two or more independent indicating systems (one of which may be audible) and limit energy input to the detector by the circuitry used. An example is a 2-pole voltage detector, i.e. a detector unit with an integral test probe, an interconnecting lead and a second test probe.  These detectors are designed and constructed to limit the current and energy which can flow into the detector. The limitation is usually provided by a combination of circuit design, using the concept of protective impedance, and current limiting resistors built into the test probes. These detectors are provided with in-built test features to check the functioning of the detector before and after use. The interconnecting lead and second test probe are not detachable components. These types of detector do not require additional current limiting resistors or hbc fuses to be fitted provided that they are made to an acceptable standard and the contact electrodes are shrouded.

Safety in use of Electrical testing equipments (rated voltages less than 650V) .......2

Design safety requirements for Test probes and leads :-

The test probes and leads used in conjunction with a voltmeter, multimeter, electrician’s test lamp or voltage indicator should be selected to prevent danger. Good test probes and leads will have the following:

(      (a)  The probes:-

(i) Have finger barriers or are shaped to guard against inadvertent hand contact with the live conductors under test;

(ii)  Are insulated to leave an exposed metal tip not exceeding 4 mm measured across any surface of the tip. Where practicable it is strongly recommended that this is reduced to 2 mm or less, or that spring loaded retractable screened probes are used;

(iii) Should have suitable high breaking capacity (hbc), sometimes known as hrc, fuse, or fuses, with a low current rating (usually not exceeding 500 mA), or a current-limiting resistor and a fuse.

 (b) The leads:

(i) Are adequately insulated (choice of insulating material may be influenced by the environment in which the leads are to be used);

(ii) Are coloured so that one lead can be easily distinguished from the other;

(iii) Are flexible and of sufficient capacity for the duty expected of them;

(iv) Are sheathed to protect against mechanical damage;

(v)  Are long enough for the purpose, while not too long so that they are clumsy or unwieldy;

(vi) Do not have accessible exposed conductors other than the probe tips, or have live conductors accessible to a person’s finger if a lead becomes detached from a probe, indicator or instrument when in use. The test lead or leads are held captive and sealed into the body of the voltage detector.

Safety in use of Electrical testing equipments (rated voltages less than 650V) .......1

Unsuitable test probes, leads, lamps, voltage indicators and multimeters have caused arcs due to:

(a)  Inadequately insulated test probes (typically having an excessive length of bare metal at the contact end) accidentally bridging a live conductor and adjacent earthed metalwork; or

(b)  Excessive current drawn through test probes, leads and measuring instruments. This happens when a multimeter is set to the wrong function, eg set on a current or resistance range when measuring voltage.

(c)  Inadequate insulation of test leads and probes;

(d)  Exposed live terminations at instruments and indicators;

(e)  A lead falling off one of the terminals of a meter and either the meter terminal or the lead terminal remaining live;

(f)   Incorrect use of test equipment, eg a multimeter applied to conductors at a voltage which exceeds the maximum working voltage of the instrument;

(g)  Use of poorly constructed makeshift test equipment, eg a test lamp consisting of a combination of a bayonet lamp holder, bulb and two single insulated conductors with bared ends;

(h)  Use of long intertwined leads which were not easily distinguished, resulting in one lead being connected across the instrument and the other short circuiting the live conductors under test.