Diesel Generator Glossary / Jargon Buster

When researching diesel generators, we know that the terminology can get quite confusing at times. Thankfully, AMPS have recently published their jargon buster for all things diesel generators, and we have every single term below. We suggest you bookmark this page, and if you're ever unsure about some terminology, you know you have a fantastic source at your finger tips.

Hyundai DHY6000SELR

Air circuit breaker – Circuit breaker contacts open to the air (atmosphere).

AC generator – Electrical generator that produces alternating current (preferred term), aka alternator.

Active power – AC power with a unity power factor. Measured in watts.

Alternator – Electrical generator that produces alternating current (non-preferred term).

Amotrisseur winding – Winding embedded in the pole face of a synchronous generator, whose function is to dampen oscillations of the pole due to cyclic irregularity and effect of lad changes.

Ampere – The unit of electrical current (Amp).

Analogue controls – Controls using variable voltage or current to pass information.

Apparent power – The produce of current and voltage in an alternating current circuit which has a reactive element.

Armature – The assembly of windings and iron core in which the generator output is produced. Sometimes referred to as the Stator to avoid confusions.

Asynchronous – Term applied to motors or generators which operate at a speed not fixed by poleage and the supply frequency.

Attenuators – Devices for reduction of the emission of sound (also known as silencers)

Automatic transfer swtich – A device used to automatically switch a power supply from normal to emergency when a power failure occurs.

Auto transfer starter – Transformer switching arrangement to reduce voltage applied to an electric motor during starting.

AVR droop – AVR Voltage Reference is reduced as Load increases.

Backup protection – Type of protection intended to operate only after the main protective device(s) has failed to operate.

Base load – The portion of load of a generator or building which is constant.

BioDiesel - Diesel fuel with all or part content derived from vegetable oils.

Black start – Refers to starting of a power system without the use of an external power source, i.e. the building or application.

Brown out – An intentional or unintentional drop in voltage in the utility mains power supply. Intentional brownouts are used for load reduction in an emergency. The reduction may last for minutes or hours, as opposed to short-term voltage sag (or dip)  lasting seconds caused by other factors. It is known that such voltage drops can be harmful to certain sensitive electrical devices, such as computers; therefore accentuating the importance of a resilient back up regime including a generating set for business.

Bulk tank – A large storage tank from which the generating set may take its immediate supply of fuel or may be used to provide a supply to a dry tank.

Bunding – This relates to the provision for containing leakage of fuel, contaminated water, oil, etc.

Busbar – Copper or aluminium (usually rigid) conductors of rectangle, square, round, or hollow section, to inter-connect high current circuits in a switchboard or building.

Circuit – An electrical circuit is an interconnection of electrical elements such as resistors, inductors, capacitors, transmission lines, switches etc. with a power source and a closed loop return path for the current.

Circuit breaker – A protective device to automatically interrupt the flow of current in a circuit when the current level exceeds a certain value.

Close-fit – A generic term for an enclosure of canopy which is designed to fit onto the base frame of the generating set; these may be sound proofed or simply weather protected.

Combined Heat and Power (CHP) – Use of a generating set or sets for the purpose of utilising the heat produced (via the exhaust and the radiator) as well as producing electricity.

Compound generator – A generator whose excitation system takes element of both voltage and current, or derivatives of these in order to give the required level of excitation to the main field.

Contactor – An electrically operated heavy current switching device.

Cross current compensation – System whereby the current loading of a generator in parallel with another is used to adjust the excitation of the second generator, so that the two generators share the load equally, with minimum impact on the combined voltage level.

Current transformer – A current transformer will produce a reduced current (usually 1 or 5 amps) in its isolated secondary circuit proportional to the current in the main circuit being measured.

Cycle – The complete reversal of an alternating current or voltage, from zero to positive maximum down to negative maximum and back to zero.

Damper winding – More common term for amortisseur winding.

Day tank – A small storage tank from which the generating set takes its immediate supply of fuel. Often 8 working hours and designed into the base frame of the generating set.

Decibels – Decibels dB and Db(A) are abbreviations for decibel, it is the “unit” for both sound pressure and sound power level. It’s not a unit because it’s the logarithm of a quotient, that’s why Lp (pressure) and Lw (power) are both expressed in dB, each with a different reference and therefore unit-less. The A is a weighing value, as in dB(A), but this is not supported by ISO standards. To be meaningful, the A must be contained in LpA or LwA and with proper description.

Deflection tolerance – Term used in specifying vibration mounts, indicating capacity to accommodate “on site” conditions.

Delta – Usually associated with a winding connection configuration of a transformer or electrical rotating machine. Where the three phase-coils are connected in a delta configuration. There are a number of connection options for both 3 and 4 wire circuits e.g. open delta, Edison delta, jack-leg delta, etc. A two coil 3 wire connection would be an Open Delta.

Deviation factor – The maximum instantaneous deviation of a generator voltage waveform, as a percentage of the true sine wave of the same RMS value.

Diesel bug – The generic term for the microbial growth found within fuel systems and fuel storage tanks. Formed of a variety of different strains of fungi and bacteria.

Diesel rotary UPS – A diesel engine driven generating set which includes an electric motor driven heavy flywheel and AC generator. In normal operation, the motor drives the flywheel/AC generator. When the mains supply fails the diesel engine is started and takes over from the motor, to drive the flywheel/AC generator. The heavy flywheel keeps the system stable whilst the engine is starting up.

Dielectric strength – The maximum electric strength that an insulating material can withstand intrinsically without breaking down, i.e. without experiencing failure of its insulating properties.

Differential protection relay – Relay operated by the current differential between two points of a series connecting electrical circuit.

Direct current – Current flow in one direction only i.e. no reversal of polarity.

Droop – Term used to describe the negative off-set of a reference (usually that of frequency or voltage) with increasing load. In the context of generating sets, the term is usually applied to the governor or automatic voltage regulator and to the speed or voltage reference respectively. Introducing a droop characteristic for frequency and voltage is one method that is used to introduce stability to generating sets operating in parallel with one another.

Double skin – The extra layer inside a fuel tank and pipework to minimise the risk of potential leakage. Equally applies to any toxic liquid around a generating set.

Dump Line – Refers to the safeguarding method of using a pipe work system to ‘dump’ fuel away from a day tank when there is a potential fire risk.

Duty assist – An arrangement where two (or more) generating sets are configured to provide mutual support in case of one piece failing to operate or needing assistance to achieve a required target: If one generating set fails to operate or cannot achieve a required target, the second (and subsequent) generating set will operate.

Duty standby – An arrangement where two (or more) generating sets are configured to provide mutual support in case of one piece failing to operate: If one generating set fails to operate, the other one will operate. One unit is duty, the other(s) is standby to the duty unit.

Earth fault – Failure of electrical insulation between live conductors and earth. May be considered for detection in “restricted” areas of a circuit or “unrestricted” i.e. occurrence of a fault anywhere within a circuit.

Electronic governor – Electronic device to control and maintain the speed of an engine. Usually done by monitoring the output of a tachogenerator or magnetic pick-up, and feeding a proportional output to an actuator which controls the engine fuel supply.

Emission level stages – European emission standard for new non-road diesel engines (fixed and variable speed).

Engine governing – Engine speed control (see Governor) which may be mechanic, hydraulic or electronic.

Engine starting – 12 or 24V electric, air, hydraulic, spring.

Exciter – A secondary generator or winding that provides DC power for excitation of the main field of a synchronous AC generator.

Exhaust silencer – Device to reduce noise level of an engine exhaust system (possibly indicatively referring to industrial or residential noise levels)

Feed and Return – Also known as Flow and Return pipes, and refers to the provision and route of a suitable pipework to the bulk fuel storage tank, where the fuel can be maintained and quality monitored. Particularly relevant with the use of biofuels where there is a potential degradation of quality if the fuel is stored for long periods of time (see “Fuel polishing”)

Field – A permanent or electromagnet whose magnetic field induces voltage in the armature coils of a generator.

Fillpoint cabinet – A cabinet, often wall mounted or free standing, with connections and equipment to allow remote filling of a fuel, or other fluid, tank.

Fire rated enclosure / section building – An enclosure constructed to meet a fire regulation i.e. BS476 4 hour fire rating or Offshore fire rating i.e. A60 i.e. 60 minutes integrity with a max temp rise from one side to other of 140 degrees.

Fire protection systems – From a simple drop weight fire valve in the fuel line to full fire suppression systems; a system is in place to react in the event of a fire; cut off the flow of combustible material (e.g. fuel) to an area or a machine and shut down the affected components of may suppress the fire with either water, foam or an inert gas.

Free field measurement – Measurement of sound in an environment in which the effect of reflective boundaries can be considered eligible.

Frequency – The number of cycles of alternating signal e.g. electrical current or sound in a given time i.e. cycles per second (Hz).

Frequency regulation – The degree of variation in steady state frequency of a generating set from no-load to fully loaded state.

Fuel lines – Pipelines from an engine to a fuel tank or from one fuel tank to another fuel tank.

Fuel polishing – The removal of water, sediment, non-combustible particulate matter and microbial contamination to below levels stated in ASTM D975 (Standard Specification for Diesel Fuel Oils) while re-suspending combustible particulate matter to maintain ASTM standards for BTU value, lubricity, and cetane number.

Full Electronic Authority Digital Engine Control – Full authority digital engine control has no form of manual override available, placing full authority over the operating parameters of the engine in the hands of the computer. It a total FADEC failure occurs, the engine fails. If the engine is controlled digitally and electronically but allows for manual override, it is considered solely an EEC (Electronic Engine Control) or ECU (Electronic Control Unit).

G59 Protection – An Energy Networks Association (ENA) document specifying the connection and protection requirements for the connection of a generator, above 16 Amps, to the Distribution Network.

Gas powered – Gas fuelled generating set – differing gas types for differing applications.

Governor – A device on the engine for controlling fuel to the engine to maintain speed under varying load conditions or a pre-set speed droop from no-load to full load conditions (electronic or mechanical)

Grid Codes – An evolving set of international standards for all forms of generators (alternators) which are aimed at better ensuring continuous and stable power supplied, and take into account the use of generator from renewable sources, as well as achieving of transmission and distribution practices.

Hall effect sensor – A method of measuring the strength of a magnetic field (by way of a transducer) that varies its output voltages in response to a magnetic field by measuring the Hall effect, which is the small voltage that is produced when a flow of electrons interacts with a magnetic field. The CT’s (circuit transformers) found in generating set control panels are a typical example sensors which reference the Hall effect.

Harmonics – A component of a periodic signal with a frequency that is a multiple of the frequency of the source signal.

Hertz – The unit of frequency measurement equal to one cycle per second.

Hunting – A term which can relate to speed or voltage, and which occurs after a control function change, causing the controlled element to continue to oscillate about the desired set value. Usually the result of insufficient damping in the control.

Impedance – Total of resistive, capacitive and inductive elements of a circuit.

Inrush current – Initial instantaneous current drawn by transformers, capacitors or current-using equipment on the application of a supply voltage. Causes of these high currents vary with different types of equipment.

Insulation – Non conductive material used between phases or phase to earth to prevent current leakage. Generally classified in terms of capability to withstand rises in temperature or dielectric strength.

IP rating – Ingress Protection. Degree of protection to ingress of particles and moisture.

Kilo-volt-ampere kVA – 1000VA. A term used for rating of an electrical circuit, which is the product of the circuit maximum current and voltage rating.

Kilo-watt kW – 1000 watts. Unit used for power rating of electrical devices.

Kilo-watt-hour – 1000 watt-hours. The unit of electrical energy equal to the use of one kW for the period of one hour.

Load acceptance - % of the rated set load that can be applied to a generator set and is capable of accepting in one step, and recovering from within defined parameters.

Load balancing – Common term used to describe best practice of balancing the load evenly across 3 phases where possible.

Load bank – Resistors and/or inductors that can be connected to a generating set either for test purposes to simulate a real load or to provide a method to absorb power where regenerative power may exceed the generator’s capability. Often mobile.

Load factor – The ratio of average load to the generating set power rating.

Load step – Normally a percentage load applied to a generating set.

Lube oil make up system – All oils consume lubricating oil when they run. Therefore, the autonomy of an engine (time for which the engine can run without requiring human interaction) is determined by how much oil in the engine is available to be consumed. To supplement this, a lube oil make up system can be added. This normally consists of a small lubricating oil tank connected to the engine with a make up valve. The make up valve provides a slow feed of oil to the engine to match the consumption of oil. It is important for any engine that the autonomy of the lubricating oil system matches or exceeds the autonomy of the fuel system.

Magnetic pick-up – A device (hall effect sensor) that detects the speed of a prime mover, typically an engine or turbine. They are the communication link between the engine and an electronic governor control. The MPU is installed next to a flywheel ring gear which is made of a material that reacts to a magnetic field. As each tooth of the ring gear passes within 0.75mm to 1.0mm of the MPU, the tooth interrupts the MPU’s magnetic field, and an alternating voltage is developed. The frequency of this voltage is translated by the speed control into a signal that accurately depicts the speed of the prime mover.

Main set breaker – The main breaker is the circuit breaker through which the full power of the generating set flows.

Mains breaker – A circuit breaker which is usually positioned at the electricity services intake of a premises and which may be interlocked with a generator circuit breaker to form a changeover from mains to generator power.

Mechanical bridge – A support for power cabling, fuel lines, exhaust, radiator, etc.

Motoring – This is the term applied when a generator remains connected to a network or other generators but its drive engine fails to delivery power – the generating set continues to run with the generator now driving the engine i.e. the generator becomes a motor.

Moulded case circuit breaker – A circuit breaker which is enclosed in a plastic insulating case and which trips when the current exceeds a pre-determined value for a given time.

Noise pollution – A term often used to refer to the inherent noise of any machines, near to buildings, people, etc, which may require treatment to reduce its effect, and maybe a key design consideration.

Non-linear load – A load in which there is a non-linear relationship between current and voltage. Commonly the result of electronic switching during the cycle in the load circuits, typically in most electronic controllers.

Normally closed / open contact – Description of the status of a relay contact when the relay is de-energised.

Octave band – Frequency range where the highest frequency is double the lowest, with eight bands 63Hz, 125H\, 250Hz etc. being used most frequently to analyse and quantify sound.

Offset fill point – Remote or low-level fill points added to tanks to make the filling process easier. This is especially recommended for tanks where direct-filling could cause safety issues (see fillpoint cabinet’)

Out-of-phase – Referring to alternating currents or voltages of the same frequency, which are not passing through their zero points at the same time.

Overload – Term referring to the amount by which an electrical circuit is exceeding its rating.

Overshoot aka Overspeed – The amount by which voltage or frequency exceeds the nominal value following a load change.

Parallel operation – Operating two or more generating sets, or generating sets and the mains, networked together to supply a common load.

Pole slip – A condition whereby a generator, or group of generators, terminal voltage angles (or phases) go past allowable (typically 90 or 180 electrical degrees) limits with respect to the rest of the connected power system.

Power factor – In AC circuits, the power factor is in the ratio of the real power flowing to a circuit (that is used to do work) and the apparent power that is available to do work in a circuit (the product of current and voltage). The power factor is a dimensionless number unrecognised by current ISO standards.

Prime power – The maximum power which a generating set is capable of delivering continuously whilst supplying a variable load when operating for an unlimited number of hours per year under the agreed operating conditions with the maintenance intervals and procedures being carried out as prescribed by the manufacturer.

Radiator – Typically, heat exchangers used to transfer thermal energy from one medium to another for the purpose of cooling fluids flowing in circuits around an engine, including the water jacket cooling the engine; a charge air circuit used to cool directly the compressed air from an engine turbo chargers, prior to entry into the engine for combustion; a secondary water circuit on engines fitted with water cooled charge air coolers.

Ratiometric – A term used in electronic circuits (or system) where the output has a direct proportional relationship to the input.

Reactance – Steady state reaction to flow of AC current.

Rotor – Rotating part of an electrical generator.

Self-excited generator – A generator whose excitation system takes power from its own output.

Short term operating reserve – A generator whose excitation system takes power from a separate source. Usually a secondary generator or exciter.

Solid state controls – Electronic control (switching) devices e.g. transistors.

Sound pressure level – Sound level in dB (or dBA) relative to reference pressure level in Pascals.

Speed droop – Governor speed reference is reduced as load (or fuelling) increases.

Starting current – High current drawn by an electronic motor during starting.

Stator – The stationary wound assembly of an AC generator or exciter.

Surge – A term applied to both current and voltage, it refers to an exceptionally high increase in the quantity over a very short time period. Usually the result of load switching or lightning strikes.

Thermostat – Device which switches at a designed temperature – used to control temperature of a medium e.g. air ambient, coolant temperature.

Transformer – May be alternating current or voltage related, the transformer is a device for changing the value of the quantity from one level to another.

Volt – The unit of electrical potential.

Voltage dip – The temporary drop in generator voltage that occurs when a load is connected, before the AVR control system responds and corrects it.

Voltage regulation – The allowed difference between maximum and minimum steady state voltage as a percentage of the nominal voltage.

Watt – A unit of power.

Zero sequence phase sequence current – Element of fault current vector with no phase sequence rotation.

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