Harmonic distortion Blackouts Under or over voltage Dips (or sags) and surges, Transients.

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1 Power Quality Standards in India Power Quality is a measure of an ideal power supply system. It can be defined as any power problem manifested in voltage, current and frequency deviations that result in mal operation or failure of customer equipment. An ideal power supply should be available at all times in the right quality. So two major dimensions arise as follows; 1. Quality 2. Reliability (24 x 7 supply) As for quality of power supply (alternating current which is widely used i.e. AC supply) conventionally it is the standard of Voltage and Frequency which defines the quality of supply. In case of DC supply systems i.e. direct current, it is the magnitude of the voltage. But with the increased digital economy the waveform of alternating current, normally a pure sinusoidal wave also became an area of concern for power quality benchmark. The most obvious defects in power supply system are complete interruption (which may last from a few seconds to several hours) and voltage dips or sags where the voltage drops to a lower value for a short duration. Naturally, long power interruptions are a problem for all users, but many critical operations are very sensitive to even very short interruptions. A typical example of a sensitive operation is the Information Technology (I.T) / I.T enabled Electronic Data processing industry, where the value of the transaction is high but the cost of processing is low; hence any failure of process is catastrophic. A perfect power supply would be one that is always available, always within voltage and frequency tolerances, and has a pure noise free sinusoidal wave shape. Power quality defects the deviations from perfection fall into five categories as below besides the above two major standards for Voltage and Frequency: Harmonic distortion Blackouts Under or over voltage Dips (or sags) and surges, Transients. 1

2 Each of these power quality problems has a different cause. Some problems are a result of the shared infrastructure. For example, a fault on the network may cause a dip that will affect some customers and the higher the level of the fault, the greater the number affected, or a problem on one customer s site may cause a transient that affects all other customers on the same subsystem. Other problems, such as harmonics, arise within the customer s own installation and may or may not propagate onto the network thus affecting other customers. Harmonic problems can be dealt with by a combination of good design practice and well proven reduction equipment. In India IE rules 1956 defines the standard for voltage and frequency at clause as follows: 54. Declared voltage of supply to consumer-except with the written consent of the consumer or with the previous sanction of the State Government, a supplier shall not permit the voltage at the point of commencement of supply as defined under rule 58 to vary from the declared voltage: (i) in the case of low or medium voltage, by more than 6 per cent, or; (ii) in the case of high voltage, by more than 6 per cent on the higher side or by more than 9 percent on the lower side, or; (iii) in the case of extra-high voltage, by more than 10 per cent on the higher side or by more than 12.5 per cent on the lower side. 55. Declared frequency of supply to consumer:-except with the written consent of the consumer or with the previous sanction of the State Government, a supplier shall not permit the frequency of an alternating current supply to vary from the declared frequency by more than 3 percent. The above standards have been observed by the utilities, mostly public and vertically integrated, in India since past few decades but with the introduction of the Electricity Act 2003 respective State Electricity Regulatory Commissions (SERC) are mandated to prescribe both Conditions of Supply and Standards of Performance for distribution utilities. Many of the state regulators have already issued such electricity supply code 1 and standard of performance regulations 2 which puts onus on the utility to observe not only the above qualities of supply but also various reliability indices like SAIDI, SAIFI, CAIDI, CAIFI etc in line with IEEE guidelines. Few progressive States also has prescribed standards for Harmonic distortion limits in line with IEEE 519 but halted from implementation due to absence of quality metering at cost effective point

3 Similarly at the transmission level or Grid level the central regulator (CERC) has prescribed various voltage distortion limits (see table 1 below), in line with IEEE standard, under India Electricity Grid Code 3. Table Harmonic Voltage Limits Voltage Distortion Limits Bus Voltage at PCC Individual Voltage Total Voltage Distortion Distortion (%) THD (%) 69 kv and below kv through 161kV kv and above NOTE : High-voltage systems can have up to 2.0% THD where the cause is an HVDC terminal that will attenuate by the time it is tapped for a user. The Central Electricity Authority (CEA) of India has prescribed Central Grid Code 4 which specifies the steady state voltage variation limits, maximum permissible values of voltage unbalance and harmonic standards as given below (see table 2) System Voltage (Nominal) kv rms Table 2. Voltage Variation Limits and Harmonic Standards as in Central Grid Code. Voltage Variation (%) Voltage Unbalance (%) Total Harmonic Distortion (%) Individual Harmonics of any particular frequency (%) / - 3% / - 3% / - 5% and below + / - 10% Various power quality standards those are likely to be observed in India to deal with transients etc are mostly in line with IEEE standards depicted in the table 5 below (see table 3 overleaf): (Draft Grid Standards Regulation) 5 Ref: Power Quality Primer Barry W. Kennedy, McGraw Hill Professional,2000 3

4 Topics Grounding 446 Powering ANSI CS4.1 [B65] Surge protection IEEE C62 series [B93] Harmonics IEEE C [B90] Disturbances ANSI C [B91] Life/fire safety FIPS PUB94 Mitigation 446 Equipment Telecommunications FIPS PUB94 equipment Noise control FIPS PUB94 Utility interface 446 Monitoring 1100 [B87] Load immunity 141 System reliability 493 [B77] is this standard. Table 3 Power quality standards by topic [B79] 1100 [B87] ANSI/NPFA 70 [B67] 1035 [B85] 487 [B76] 518 [B78] 929[B83] 1159 (see note f) 446 Relevant standards 142 [B71] [B71] IEEE P519A [B80] NFPA 75 [B96] 1050 [B86] 1001 [B84] NFPA 78 [B97] 929 [B83] UL 1478 [B17] 1035 [B85] ANSI/NPFA 70 [B67] UL 1449 [B99] 1001 [B87] UL 1950 [B18] NEMA-UPS [B94] IEEE P1346 [B89] Similarly the current distortion limits for general distribution systems are observed in line with IEEE standards as given in Table 4 below. Table Harmonic Current Limits Current Distortion Limits for General Distribution Systems (120 V Through V) Maximum Harmonic Current Distortion in Percent of IL Individual Harmonic Order (Odd Harmonics) ISC/IL <11 11 h<17 17 h<23 23 h<35 35 h TDD <20* < < < > Even harmonics are limited to 25% of the odd harmonic limits above. Current distrortions that result in a dc offset, e.g. half-wave converters, are not allowed. * All power generation equipment is limited to these values of current distortion, regardless of actual ISC/IL Where ISC = maximum short-circuit current at PCC. IL = maximum demand load current (fundamental frequency component) at PCC. TDD = Total demand distortion (RSS), harmonic current distortion in % of maximum demand load current (15 or 30 min demand). PCC = Point of common coupling. 4

5 In addition to above Voltage, Current and Harmonics related standards and regulations observed at various levels, various Indian Standards for individual product categories are observed in line with IEC standards. Few of them also follow ANSI standard for grounding etc. CBEMA curve or ITIC curves are followed as standard in Computer business equipments and or Information Technology equipment. One key utility regulation observed across India today is limit of power factor i.e. the indicator of reactive power consumption from the grid; often the cause of poor voltage regulation. However this is mostly decided by the respective State Electricity Regulatory Commissions (SERCs) as part of the tariff regulation by designing a retail tariff that either incentivise or penalize the customer based on benchmark power factor to be observed during the billing month. Some of the distribution utilities are even adopting kva based demand charges as part of two part tariff system to ensure consumer discipline while connecting to the grid. Recently the utilities are exploring avenues and metering feasibility to adopt kvahr based billing instead of monthly kva and kwhr based billing. In recent times with telecom revolution in India the effect of EMI/ EMC is getting more attention and efforts are on to introduce standards in this area in line with IEC or BS standards. --X-- Authored by Manas Kumar Kundu, International Copper Promotion Council (India), Mumbai, India. Date: January