DG Set and Power Backup Glossary
kVA (kilovolt-ampere). The apparent power a generator can deliver. It is the figure gensets are sold and specified by, and it accounts for the total current the alternator must supply, including the portion that does no useful work.
kW (kilowatt). The real power a generator delivers, meaning the power that does actual work. kW is what your load consumes. kW equals kVA multiplied by the power factor, so at 0.8 power factor a 100 kVA set delivers 80 kW. Specifying against one figure when your load is stated in the other is a common source of sizing error.
Power factor. The ratio of real power to apparent power, expressed as a decimal between 0 and 1. Diesel generator sets across the Mahindra Powerol range are rated at 0.8 power factor lagging. Loads with a large inductive component, such as motors and transformers, reduce the power factor and increase the current the alternator must supply.
ESP (Emergency Standby Power). The rating for sets used only when mains supply fails. Variable load, no overload permitted. Mahindra Powerol publishes standby power as limited to 500 hours annual usage with an average load factor of 80% of the published standby rating over each 24-hour period, of which up to 300 hours may be run continuously. The usual rating for commercial and institutional standby installations.
PRP (Prime Rated Power). The rating for sets running unlimited hours on a variable load. Mahindra Powerol publishes prime power as unlimited hours at an average load factor of 80% of the published prime power over each 24-hour period, with a 10% overload available for one hour in every twelve hours of operation.
LTP (Limited-Time Running Power). The ISO 8528-1 rating for sets running at up to full load for a restricted number of hours per year, with no overload capability. Applied to peak shaving and load curtailment.
COP (Continuous Operating Power). The ISO 8528-1 rating for sets supplying a constant load for unlimited hours with no overload capability. Also called base load rating. Not to be confused with Conformity of Production, a CPCB emissions certificate that shares the acronym.
Block loading and step loading. Block loading means applying load to a generator in a single step. Step loading means applying it in staged increments, which reduces transient demand on the engine and can allow a smaller set to serve the same total load, provided the panel sequencing is designed for it. Block loading capability is stated as a percentage of prime rating within a governing class under ISO 8528-5. The Perkins 2806FA-E18TAG1 used in the 525 kVA set accepts 55% of prime within class G2, and the TAG2 used in the 650 kVA set accepts 50%.
Governing class. The engine speed governing performance class under ISO 8528-5, expressed as G1 to G4. Higher classes hold frequency more tightly during load changes. Sets in the Mahindra Powerol range are specified as G2 or G3.
Step loading. Applying load in staged increments. Reduces the transient demand on the engine and can allow a smaller set to serve the same total load, provided the sequencing is designed for it.
Derating. The reduction in a genset's usable output caused by site conditions such as altitude, ambient temperature and restricted ventilation. A derated set will not deliver its nameplate rating.
AMF panel (Auto Mains Failure). Senses loss of mains supply, starts the generator, transfers the load, and reverses the sequence when mains returns.
ATS (Automatic Transfer Switch). The switching device that moves the load between mains and generator supply. Built into the AMF panel on smaller installations, a separate device on larger ones.
Synchronising panel. Matches the voltage, frequency and phase of two or more generators so they can share a load in parallel. Required for any multi-set installation.
LT panel (Low Tension panel). The low voltage distribution panel through which generator output reaches the building's electrical system.
Megger test. An insulation resistance test carried out before energisation. Under the CEA (Measures relating to Safety and Electric Supply) Regulations, 2023, testing and verification is to be carried out as per the relevant standards, and testing equipment must be calibrated by a government authorised or NABL accredited laboratory. The specific 1 megohm at 500 V DC threshold set out in the superseded 2010 Regulations no longer appears in the regulations themselves.
Body, neutral and lightning earthing. Three separate systems serving separate purposes, not interchangeable. Body earthing protects personnel: CEA Regulation 43(vii) requires the frame of every generator, and other apparatus above 250 V but not exceeding 650 V, to be earthed by two separate and distinct connections. Neutral earthing sets the system reference and allows earth fault protection to operate: Regulation 43(xiii) requires the neutral point to be earthed by no fewer than two separate and distinct connections. Lightning earthing protects the installation and the exhaust stack structure from strike.
Earth leakage protection. Under CEA Regulation 44, the use of electricity in an electrical installation must be controlled by a residual current device, with rated residual current and duration as per the relevant standards. For domestic installations the residual operating current must not exceed 30 milliamperes. The 100 milliampere figure for non-domestic installations appeared in the superseded 2010 Regulations and is not carried into the 2023 Regulations.
dB(A). The A-weighted decibel, a sound level measurement adjusted to reflect how the human ear responds to different frequencies. All Indian genset noise limits are expressed in dB(A).
Leq. The energy mean of a noise level over a specified period. Ambient noise standards in India are expressed as dB(A) Leq rather than as instantaneous peaks.
Acoustic enclosure and acoustic room treatment. Two routes to the same requirement. An acoustic enclosure is a sound-attenuating canopy built around the set; under GSR 371(E), new diesel sets up to 1000 kVA must be fitted with an integral enclosure at the manufacturing stage and are limited to 75 dB(A) at 1 metre. Acoustic room treatment applies the same barrier and absorption principles to the walls, ceiling and ventilation paths of the DG room, and is used where a set cannot practically be canopied.
Insertion loss. The reduction in sound level achieved by adding an enclosure, room treatment or muffler, expressed in dB(A). CPCB requires enclosures and room treatment to be designed for a minimum of 25 dB(A) insertion loss, or to meet ambient noise standards, whichever is higher. Measured at several points 0.5 metre from the enclosure and averaged. Exhaust silencer insertion loss is measured under ISO 15619.
Sound power level and sound pressure level. Two different quantities that datasheets often conflate. Sound power level is a property of the machine and does not vary with distance. Sound pressure level is what a meter reads at a given point and falls as distance increases. The 75 dB(A) statutory limit is a sound pressure level at 1 metre. Type testing measures sound power level.
ISO 8528-10. The noise test code for engine-driven generating sets, using the enveloping surface method, adopted in India as IS/ISO 8528-10 by the Bureau of Indian Standards. Sound power level for CPCB noise conformance is measured under this standard together with ISO 3744. Its scope excludes exhaust and cooling noise where those systems are ducted to a remote point.
Enclosure types. Integrated enclosures are factory-fitted and bottom-lifting. Drop-down enclosures are assembled on site from separate panels, used where access will not permit delivery of a complete canopied set. Containerised enclosures are fully welded and top-lifting, built on ISO container principles.
Ambient noise standards. The permissible noise limits under the Noise Pollution (Regulation and Control) Rules, 2000, applied by state pollution control boards through consent conditions. In industrial areas, 75 dB(A) Leq by day and 70 by night. In commercial areas, 65 and 55. In residential areas, 55 and 45. In silence zones, 50 and 40. Day means 6 am to 10 pm and night means 10 pm to 6 am.
CPCB IV+. The emission standard for genset engines up to 800 kW gross mechanical power, notified vide GSR 804(E) dated 3 November 2022 as the Environment (Protection) Third Amendment Rules. Replaced the earlier CPCB II norms.
Type Approval and Conformity of Production certificates. Type Approval certifies that an engine type or family meets the applicable emission limits. Conformity of Production certifies that production units continue to meet the standard the type was approved against, and is issued per COP year running 1 July to 30 June. Both are issued by CPCB-approved agencies, currently ARAI Pune, ICAT Manesar and the Indian Institute of Petroleum, Dehradun. No genset containing an engine may be sold, imported or used in India without both.
CEA Safety Regulations 2023. The Central Electricity Authority (Measures relating to Safety and Electric Supply) Regulations, 2023, notified on 8 June 2023 in supersession of the 2010 Regulations of the same name. Made under section 177 of the Electricity Act 2003. Sets the earthing, testing, clearance and inspection requirements a DG installation must meet.
CEIG (Chief Electrical Inspectorate). The state authority responsible for electrical safety approval of installations. Under CEA Regulation 34, the capacity above which generating units must be inspected before commissioning is fixed by state notification, so the threshold varies by state. Each state also notifies a voltage up to which self-certification may replace inspection, under Regulations 32 and 45, with the report submitted to the Electrical Inspector's office.
Chartered Electrical Safety Engineer. A person authorised by the state government under CEA Regulation 6 to assist an owner, supplier or consumer with self-certification of an electrical installation. Introduced by the 2023 Regulations.
CFE and CFO (Consent for Establishment and Consent for Operation). Two pollution control board consents granted under the Water Act 1974 and the Air Act 1981. CFE is obtained before the installation is built, sometimes called Consent to Establish. CFO is granted after the board inspects the completed installation, under section 25(4) of the Water Act and section 21 of the Air Act, and authorises operation. Consent orders specify the minimum chimney height for each DG set and require acoustic enclosures as the noise control measure.
KSPCB. Karnataka State Pollution Control Board, which administers CFE and CFO for installations in Karnataka and categorises industries as red, orange or green.
PESO and Petroleum Class B. The Petroleum and Explosives Safety Organisation administers the Petroleum Act 1934 and the Petroleum Rules 2002. High speed diesel is a petroleum Class B product, exempt from licensing only up to 2,500 litres in drums or 1,000 litres in a tank. Class C, covering furnace oil and LDO, carries a much higher threshold and is frequently confused with it.
Electrical Safety Officer. A designated officer required under CEA Regulation 5 for every electrical installation with more than 250 kW connected load, and for mines and oil fields with more than 2,000 kW. Must hold an electrical engineering degree with at least five years of operation and maintenance experience, or a diploma with at least ten, and must inspect the installation at intervals not exceeding one year, keeping records available to the Electrical Inspector.
Stack height. The required height of the exhaust discharge point, governed by CPCB guidelines and specified per installation in the pollution control board's consent order, expressed as a minimum height above ground level.
Turnkey project. Complete execution of a DG installation by one contractor, from supply through installation, statutory approvals and commissioning to handover, under a single contract.
High side and low side. The two halves of a DG project scope. High side is the supply: the generator set, acoustic enclosure, AMF, ATS, synchronising and LT panels, and associated electrical equipment. Low side, also called balance of plant, is the site construction: exhaust, fuel systems, earthing, cabling, acoustic treatment and structural work. Low side is usually the larger share of both cost and risk.
Pre-commissioning and commissioning. Two distinct stages. Pre-commissioning happens before the set is first run and covers mechanical and electrical inspection, tightness checks, insulation resistance, earthing verification, and fluid and battery checks. Commissioning is running the set and proving it: engine starting, alternator testing, protection checks, load testing, AMF testing and panel testing.
AMC (Annual Maintenance Contract). A service agreement covering scheduled maintenance, and depending on the contract, breakdown attendance, spares and response time commitments.