Everything you need to know about Power Generator products
Trying to wrap your head around Genset products? The summaries below provide some outlines about what they are, how they work and how to use them, so you’ll be able to decide which of the versatile sets will best suit your needs.
What is a generator set?
A generator set – referred to simply as a Genset – combines an internal combustion engine with an electrical generator (alternator) mounted together to form a single piece of equipment.
It is an electromechanical machine used to convert thermal energy produced by combustion into an AC electrical current through a double-cascade converter: from thermal energy (introduced by diesel fuel) to mechanical energy by means of reciprocating motion (engine rotation) and from mechanical energy to electric energy (rotation of the alternator).
Generator operating modes
A) Island mode operation
This Genset is the only source of energy being used to power equipment when the public distribution network is not available or where the user decides to produce energy for their own needs without accessing the network.
Rural and remote areas, and worksites are typical applications for an island mode operation.
B) Generator standby operation
When it’s vital that energy is always available, the generator in standby operation provides the safety net for times when the distribution network has a power cut. The Genset is connected to an Automatic Transfer Switch panel so that during an unexpected black-out, the Genset will automatically switch on to provide power.
The scope of supply is any industry or business that cannot afford down time.
C) Parallel mode operation
When a Genset is the only source of energy (island mode), several units are used in parallel to provide the load as required. This provides the solution for several scenarios.
There may be a need to continuity of service; if one Genset fails or is down for maintenance, the load is still guaranteed by the other Genset/s.
Capacity may be the consideration. Some situations require more power than can be provided by a single unit, and other situations have peak periods that require additional Gensets working in parallel with smaller units to provide that extra energy when needed.
D) Parallel mode with the network
In this example, Gensets can operate in parallel mode and with the distribution network. This arrangement is typically used to compensate for absorption peaks not supported by the network or to achieve energy exchanges with the network distributor, in the case of self-powered units.
Generator performance classes
Genset performance classes are defined in ISO8528. In addition to the basic machine and manufacturer data, to comply with the above standard, each Genset must have a rating plate which lists both the electrical and mechanical quantities, as well as the ambient reference parameters.
Basic electrical quantities of the power generator are current and voltage.
Electric current is measured in Amperes [A] and represents, in physics and electrical engineering, the electric charge passing through a cross-section of wire in a unit of time. Electric current can be either direct or alternating. Gensets normally produce alternating current.
Electric voltage is measured in Volts [V] and the difference in electric potential between two points. Voltage is generated by charge separation, and it is the electromotive force which generates the current.
Electric power is measured in Watts [W] and is defined as the electrical work carried out on an electric load by an electric field within a unit of time; simplification is provided by multiplying current X voltage, or rather P=I*V.
Basic electrical quantities of the power generator:
Production system
Electricity can be generated by either a single-phase or a three-phase system. The single-phase system for distributing AC electricityis the least complicated system ,which consists of only two conductors: a neutral conductor with no potential and an active phase conductor with a sinusoidal potential that changes over time.
A three-phase system has a three-circuit alternating current (the production, distribution and use of electricity) with the same ISO frequencies, and thee equal, alternating voltages, though offset by 120°.
Basic electrical quantities of the power generator:
The frequency
Frequency is measured in Hertz [Hz] and is a basic quantity of alternating currents. For historical reasons, there are two world standards for power system frequency: 50 or 60 Hz.
There are still countries which, according to area, operate at different frequencies. The electric frequency generated by a Genset is directly proportional to engine rpm and the number of poles on the alternator.
Electrical power
Understanding electrical power will help when selecting a Genset. It can be thought of as physical labour – how much work can I do within a specific amount of time? A Genset’s electrical power is intended as the net power available at the power outlet terminal board, minus the power used by the auxiliary systems essential for its own operation (e.g. cooling fan).
There are two types of electrical power:
1) Apparent Power
Measured in VoltAmpere (VA) and symbolised by a capital ‘S’, it is the theoretical power which can be absorbed by the generator terminals. The efficiency of the load will determine how much of this will transform into work.
2) Active Power
Measured in Watts [W] and symbolised by the capital letter ‘P’, it is the power which physically transforms into work. ‘P’ depends on the load and its capacity to transform as much apparent power into active power as possible. The ratio between active power and apparent power is defined as a power factor or ‘cosf’ and the formula which regulates them is P=S*cosf.
If the load is unknown, how can the active power of a Genset be declared?
By agreement, ISO8528 specifies that the nameplate of a Genset refers to cosf=0.8. In reality, the cosf of a load can be variable and also change as a function of the work phase. For example, it can be different in an electric motor during the start-up phase compared to when it is in full operation.
For systems generally, a low utilities power factor creates drawbacks which affect not only performance, but also the costs of operating the system. In fact, a low cost results in a decrease in the power available to supply the systems or an over-sizing of systems with the same active power.
Power ratings
The reference power ratings will determine the type of use for which a Genset is applicable. The rating must be defined on the nameplate affixed to the Genset. The power ratings are themselves governed by ISO8528-1.
COP: Continuous Operation Power
This is the maximum power a Genset can supply during continuous service, with a constant load for an unlimited number of operating hours, in the ambient conditions determined by the manufacturer and observing the maintenance intervals established by the manufacturer.
PRP: Prime Power
This is the power a Genset can supply during continuous service over an unlimited number of hours with a variable load, in the ambient conditions determined by the manufacturer and observing the maintenance intervals established by the manufacturer.
The average power delivered over a 24-hour period must not exceed X% of the PRP power listed on the nameplate, where X is determined by the engine manufacturer.
An overload of Y% is permissible at regular intervals, with the value of Y and the time intervals determined by the engine manufacturer. X is typically 75% while Y is set at 10%, however these values may lower.
LTP: Limited Time Power
This is the maximum power a DEUTZ Genset can supply for an operating period, limited to 500 h/year in intermittent mode, or 300 h/year in continuous mode, in the ambient conditions determined by the manufacturer and observing maintenance intervals established by the manufacturer.
Ambient conditions of reference
All of the performance parameters mentioned above must be declared with the ambient conditions of reference. ISO8528 also gives indications in this instance. Typical reference values are:
- temperature 25°C
- altitude 100 m.a.m.s.l.; relative humidity 30%
- atmospheric pressure 100kPa.
Machine documentation must list the ambient conditions in which the machine can operate without downgrading. A reduction in performance will occur if the conditions vary from those indicated.
To establish the downgrading of the machine, the performance of main components in ambient conditions as foreseen by the Genset manufacturer must be taken into account.
Depending on the situation, this downgrade can be obtained either by using an analytical table or empirically through special testing.
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