PREVENTIVE MAINTENANCE

Protective gear and the associated control & switchgear are intended to protect expensive electrical equipment. With proper care protective, control & switchgear will perform this duty, but when neglected they may become inoperative and could become a hazard in themselves. Since the reliability is the most important quality of protective relays it follows that their maintenance must be first class.

Although protective gear and the associated control & switchgear may be in sound condition when first put into service, many troubles can develop unchecked and unrevealed because of its infrequent operation. Many of the protective gear manufacturers advise to inspect and test the protective gear at regular intervals, around 6 - 12 months. In practice, the frequency of testing may be limited by lack of staff or by the operating conditions on the power system.

It is generally accepted that protective relays and their trip circuits should be periodically checked in order to ensure that they will always be ready to operate with certainty. The recommended practice is to carry out three types of test:

• Acceptance tests at the installation or commissioning of the relays.
• Periodic tests to check the calibration and condition of the relay.
• More frequent tests of a simple nature to cause movement of the parts, and to check the continuity of the trip circuit.

Since protective gear differs from all other forms of electrical plant and equipment and is solely concerned with fault conditions it cannot readily be tested under actual operating conditions, as can other kinds of plant, nor is it feasible as a general rule to reproduce the conditions under which it will be called upon to fulfill its active, or positive, function. Many forms of protective gear, in addition to their sensitivity to pick-up during fault, have a negative function to fulfils, namely that to select the types of fault and be stable when faults occur outside the zones they are intended to protect.

Maintenance tests may sometimes have to be made when the protected equipment & circuit is on load. The particular element or scheme to be tested should be taken out of service, and adequate back-up protection provided for the duration of the tests. Such back-up protection may not be fully discriminate, but it is sufficient for it to be capable of clearing any fault on the apparatus whose main protection is temporarily out of service. However, it is desirable to carry out maintenance on protective gear at times when the associated power apparatus is out of service.

A report of the C.I.G.R.E relay study committee indicates that the order of likelihood of failure of equipment is as follows,

• Relays : 43%
• Circuit Breakers : 13.5%
• AC Wiring/ Cabling : 12%
• CB Trip Mechanism : 7%
• Current Transformers : 7%
• DC Wiring (Including trip circuits) : 5%
• Voltage Transformers : 3%
• CB Auxiliary Switches : 3%
• CB Trip coils : 2.5%
• DC Supply : 1%

Most common reasons for the failure being:

• Limitations in protection design.
• Faulty relays.
• Defects in the secondary wiring.
• Insulation failure.
• Incorrect connections.
• Incorrect settings
• Faulty pilot wires.
• Various other causes, such as switching errors, testing errors and the operation of relays from mechanical shock.

Power gear require careful handling of the equipment. The testing engineer should be entirely familiar with the protective schemes, its application, and principle of operation, design features and characteristics. He should also have knowledge of proper operating instructions provided by the manufacturers of the equipment and the guidelines stipulated by International Standards specifications.

The agency which performs the testing shall be of independent one and shall have the entire infrastructure, like Primary and Secondary Injection Test kits, Insulation Tester, Polarity Tester, Turns Ratio Test kits, Micro-ohm Meter, Current, Voltage and Resistance Measuring Instrument and above all the provision of proper Relay tool kit. INEL POWER Group of Companies Shall have all the infrastructure for Primary and Secondary Injection Tests, Insulation, Winding and Contact Resistance Tests, Polarity and Vector Group Tests, Turns Ratio Tests, and so on. They have wide range of experience in testing protective gear, control and switchgear and power gear.

INEL POWER Group of Companies . will approach the job as per the guidelines for maintenance and field testing of electrical relays and other IEC specifications for various codes of practices for various equipment. With the readily available instruction & operating manuals of various equipment, technical books and literatures, IEC specifications and other software like electrical diagrams. INEL POWER Group of Companies can perform quality related engineering service at excellence to the full satisfaction of the customer.

Testing / Maintenance:

• Circuit Breaker Retrofitting & Rebuilding
• Circuit Breakers - Air / Oil / Vacuum
• Switchboard Modifications & Repairs
• Solid Sate Conversions / Trip Units
• Disconnect Switches / Load Break Switches
• MCC / Starter Rebuilding & Overhaul
• Vacuum Retrofitting / Conversion
• Switchboard Control Wiring
• Switchgear Painting Services
• Trip Unit Repairs
• Switchgear / MCC Protection Upgrades
• Motors and Earth pits

Repairs / Upgrades Generator & Control Modifications:

• Substation Start-up Services
• Transformers / Oil Analysis
• Circuit Breakers / Switches / Switchgear
• Cable Testing Services
• Vacuum / Gas / Oil Circ. Breakers
• Motor Control Centers / Starters
• Protective Relay Calibration
• Switchgear Training Services
• DC Hi pot Services / Fault Locating
• High Current Testing / Trip Unit Calibration
• L.V.& M.V. Bus Duct Testing
• Generator, control panel, generator earthing system
• HV/LV Cable laying

TESTING EQUIPMENTS AVAILABLE

• Primary Test System (Omicron CPC 100).
• Automatic 3 Phase Relay Test Kit (Omicron 256+, 356) to Test Numerical Relays.
• CT Analyzer - Omicron for CT Testing.
• Automatic 3 Phase Relay Test Kit (FREJA 300, SVERKER 900) to Test Numerical Relays.
• Automatic Single Phase Relay Test Kit (SVERKER 750, 760, 780) to Test Numerical Relays.
• HV Capacitance & Tan Delta Test Kit to Test Power Transformer, Generator.
• Contact Resistance Measurement (Micro Ohm meter) with 200A DC Source.
• Transformer Winding Resistance Meter with 10A DC Source.
• Primary Current Injection Test Kit (ODEN ATS) upto 2000A for CT Ratio Test.
• Circuit Breaker Analyzer for Breaker Timing Test.
• 3 Pole / 1 Pole time Interval Meters for Breaker Timing Test.
• Digital / Motorized Insulation Resistance Tester upto 10KV.
• 3 Phase Energy Meter Test Kit for Energy Meter Testing.
• On Line Power Analyzer to check LV/ MV System Load Details.
• 50kV & 100 KV AC HV Kit for Testing of Switchgear Panels up to 33KV System.
• 60KV VLF High voltage test kit for XLPE Cables up to 33KV Level.
• Single Phase Automatic / Manual Relay Test Kit for Testing Numeric / Static / Electromagnetic Relays.
• Transformer Oil Filtration Machine.
• LCR Meter.
• Frequency Generator.
• Continuously variable DC Power Source.
• DC Power Source.
• Digital Power Analyzer.
• Static Phase Shifter.
• Power Quality Analyzer, HIOKI Make.
• 3 Phase 35KW Resistive load bank.
• Digital Multimeters, Clamp Meters etc.
• Digital Thermo Hygrometer
• Galvanometer
• Multifunction Process Calibrator
• Auxiliary Test Kit
• Phase Sequence Indicator
• Digital Earth Tester
• Single Phase & Three Phase Dimmer Start
• Loading Transformer
• Step-up Transformer
• HV Transformer
• 3kVA AC Hipot Kit

World Class Testing Equipment