Power system protection

IR testing: IEEE-43-2013 In insulation resistance testing, when voltage applied the insulation resistance shows a low value and then increases gradually. What's the reason for this behaviour? It is the different current like Capacitor charging current, Absorption current resulting from molecular polarizing and electron drift which eventually goes to zero and only leakage current of the insulation persists. Based on this philosophy different testing sequence is practiced in general. Differential Absorption Ratio (DAR) Definition: DAR is the ratio of the insulation resistance measured at two specific time intervals, usually 30 seconds and 1 minute. Interpretation: DAR > 1.4: Good insulation. DAR between 1.25 and 1.4: Acceptable insulation. DAR < 1.25: Poor insulation, may indicate moisture or contamination. Polarization Index (PI) Definition: PI is the ratio of the insulation resistance measured at two different time intervals, typically 1 minute and 10 minutes. Interpretation: PI > 4.0 : Excellent insulation. PI between 2.0 and 4.0: Good insulation. PI between 1.0 and 2.0: Marginal insulation, requires further analysis. PI < 1.0: Poor insulation, likely indicates severe contamination or aging.

The service voltage, the rated voltage, the rated insulation level, are the three terms which define the running of the equipment to the voltage. THE SERVICE VOLTAGE The service voltage used is the voltage applied to the terminals of theequipment. THE RATED VOLTAGE The rated voltage is the maximum effect value of the voltage which theequipment can support in normal operation. The rated voltage is alwayssuperior to the service voltage and is associated with the rated insulationlevel. RATED INSULATION LEVEL The rated insulation level determines the dielectric withstand to overvoltage and impulse voltage. The external or atmospheric overvoltages appear when the lightning shockfalls onto or close to the line. The voltage wave which follows it is simulatedin the laboratory and is called the electric impulse wave. The internal overvoltage accompanies all modification which occurs in thecircuit : opening or closing circuit, the flashing or by-passing of an insulator, etc… It is simulated in the laboratory by the rated 1 mn power frequencywhithstand voltage. Remarks : the IEC 694 gives the different voltage values in paragraph its 4, and the test conditions in its paragraph 6.

AC is used for transmission because transformers can step it as much as excessive voltage for long distance, and right down to low voltage for local distribution and use. The output of energy stations comes from a rotary turbine, which via its nature is AC and therefore requires no power electronics to transform to DC Also, it's miles lots less difficult to exchange the voltage of AC electricity for transmission and distribution and the value of plant associated with AC transmission (circuit breakers, transformers and so forth) is a great deal lower than the equal of DC transmission. AC transmission offers several technical benefits. When a fault inside the network occurs, huge fault contemporary flows. In an AC device, this will become a good deal simpler t o break, because the sine wave current will evidently tend to zero in some unspecified time in the future making the modern-day easier to break.

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Standard for Wiring and Cable Marking in Substations : D Current transformers for metering and measurements E Reference voltage for instruments, metering and protection F Reference voltage for voltage control G Reference voltage for synchronizing H AC supplies and AC/DC supplies for motorized isolators and circuit-breakers J Primary DC supplies K Protection, closing and tripping circuits L Alarms and indication initiated by auxiliary switches and relay contacts excluding those for remote selective control and for general indication equipment M Auxiliary and control motor devices, governor motor, rheostat motor, generator Automatic Voltage Regulator (AVR) control, spring charging motors, transformer cooler motor control, motors for isolator operation N Tap-change control including Automatic Voltage Control (AVC), tap position and progress indication P DC tripping circuits used solely for busbar protection R Interlock circuits and Transfer circuits S DC instruments and relays, exciter and field circuits for generators T Pilot conductors between panels, independent of the distance between them, for pilot wire protection, for inter-tripping or for both U Spare cores and connections to spare contacts W Supervisory controls and analogues, energy pulsing X Supervisory alarms and indications Y Telephones NOTE: Combined letters KL are used in breaker-and-a-half schemes where Secure Supply Circuits apply.

Circuit breaker and contactor: 1. OBJECTIVE: To verify the physical condition and electrical characteristics of CB/contactors. 2. TEST INSTRUMENTS REQUIRED: Insulation tester Micro ohmmeter CB timing test kit HV test kit 3. TEST PROCEDURE: 3.1. MECHANICAL CHECKS AND VISUAL INSPECTION: • Inspect for physical damage/ defects. • Check nameplate information for correctness. • Check tightness for all bolted connections. • Check the transport lock is removed for breaker/ contactor. • Check racking mechanism for alignment and smoothness operation. • Check operation of all mechanical interlocks. • Check correct breaker/contactor position indication. • Check for correct spring status indication. • For SF6 breakers check the correct gas pressure. • Check the manual operation of breaker/contactor. 3.2. INSULATION RESISTANCE TEST: The test voltage shall be between phase to earth and across the poles. - Each phase to earth (or body). - Across the pole for each phase. The applied test voltage limits shall be as per table 4.1. 3.3. CONTACT RESISTANCE TEST: This test is to confirm the resistance of the main contacts. Inject 100A DC current through the main contact by keeping CB closed. The voltage drop across the contact is measured and resistance is calculated. In many instruments resistance will be a direct reading. Limits: The obtained values shall be compared with factory test reports or manufacturer claimed values could be taken as reference. 3.4. CB TIMING TEST: This test is to verify the open and closing time of CB contacts. The test connection circuit is shown in Fig. Measure the closing time and tripping time with timing test kit that will measure and record the time and timing diagram. Limits: The obtained close/ open time shall be compared with manufacturer reference values or factory test results. 3.5. REDUCED VOLTAGE TEST: This test is to confirm the operation of closing coil and opening coil at reduced voltage applied. Apply reduce voltage of 80% of rated voltage for closing coil and 60% of rated voltage for trip coil and operation shall be noticed. Limits: Operation shall be observed without fail. 3.6. HIGH VOLTAGE TEST: This test shall be performed as per the section explain befor . 3.7. APPLICABLE STANDARD: IEC 60056: High voltage AC circuit breakers.

What protections are used with power transmission circuits? - In the beginning, we have to know that all circuits and transformers that work in High Voltage, such as (220KV - 380KV - 500KV-132KV) have Main1, Main2, and we mean two protection devices Tow Protection Relays on them the same Protection Function and the same Setting, but each device has a separate source of nutrition from the other and the purpose is the reliability of the system where any problem occurs on the main1, whether in the feed path or Failure on the Relay, the Main2 is in service and protects the circuit Or the Adapter from any faults We note that the Protection Relays used from different manufacturers such as MiCOM, ABB - Protections are divided into two parts: - Instantaneous protections, which means that the operating time has (zero sec) such as: - 1- Differential protection of 87L lines 2- Distance protection in Zone 1 3- Directional ground leakage protection with 67N High Stage - Delay Time protections 1- Protection distances in Zone 2-3-4 2- Directional ground leakage protection at 67N Low Stage 3- Connection protection on SOTF malfunction - As for automatic reconnection, we find that it works with protections that disconnect instantaneously, while Block with protections that work with time in Delay Time and Switch Onto Fault protection - In some schemes, we find that non-directional current surge protection is also used with power transmission circuits, and the working philosophy for it is that it works as a backup for the main protections, meaning if a block occurs on the Line Differential and a block also occurs on the Distance Protection, we find that there is an activation to protect the increase of the non-directional current, and this mode is called in some Relays as the Emergency Mode, as in 7SD SIEMENS Relay

GIS LCP

Standards - Abbrevations Standards - Abbrevations l ASME – American Society of Mechanical Engineers l ASTM – American Society for Testing and Materials l IEC – International Electrotechnical Commission l ISO – International Organization for Standardization l NACE –National Association for Corrosion Engineers l FCI – Fluids Control Institute l ISA – Instrument Society of America (Now Known as Instrumentation, Systems, and Automation Society) l NEMA – National Electrical Manufacturer’s Association l CSA – Canadian Standards Association l DIN – Deutsches Institut fur Normung (German Institute for Standardization) l CEN – European Committee for Standardization l BS – British Standards

Telecommunication System – Cable Specifications

IP degree selection: • Selection of IP degree must be according to actual operating conditions based on the locations in which switchgears & panel boards are installed. • For Example: IP54 degree of protection - according to IEC standard 60529 is the answer when a distribution and motor control switchboard’s operating environment is dusty and contains damp, in some industrial and tertiary sites. • Correct selection of IP degree will highly optimize switchgears dimensions & cost. Example showing the effect of ( IP ) on deration values of C.Bs: Fig 1 Example showing the effect of ( IP ) on deration values of Busbars:Fig2

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