Glossary of Used Diesel Generator Terms


Terminology and Concepts For Electric Generators

The following list of terms and word-pictures is offered to help our clients understand the relevant terms and concepts when purchasing, maintaining and selling electric generators. While we believe that many of the following terms need only be defined for our purposes today, comparing electrical terminology to water flowing in a pipe, while not perfect, presents a good analogy of electricity. This glossary is intended for Everyman and not overly technical.

AC versus DC
A battery is direct current (DC). The polarity of a battery is always the same--positive on one side and negative on the other. In an AC system, the polarity is constantly changing every 1/60th of a second (60 times per second, or 60 Hz). The frequency of AC electronics in the US is 60 cycles per second or hertz (HZ).

A device for converting mechanical energy into electrical energy.

The strength or intensity of an electric current, measured in amperes (AMPS).

Apparent Power, Real Power, and Power Factor
Power is the measure of a system that can perform work. Water performs work when it turns the blades of a hydroelectric plant. Electricity performs work when it heats up a heating element or turns a motor. It takes power to store energy, like in capacitive or inductive devices, while these devices then release some energy, or power, at a later time. (These devices can both expend power and deliver power.)

Apparent Power (KVA)
Many generators (and most transformers) are rated in volt-amperes (VA), or thousand-volt-amperes (KVA). A 25 KVA generator (or transformer) can deliver no more than 70 amps per phase @ 208 volts before it burns out the windings. This can therefore power 25 kilowatts of heaters, but only 20 kilowatts for motors (assuming 80% power factor), because both of these loads will use 70 amps. Since the manufacturer does not know what the generator will ultimately be used for, they rate it in KVA because this indicates the maximum current regardless of the load's power factor.

Battery Charger
A battery charger converts household electricity to direct current needed to recharge a battery. Direct current has polarity. The amount of electricity the charger puts into the battery is measured in amperes and is shown on the ammeter built into most chargers. The charging begins on a dead battery with a large amount of current going into the battery so the chargers ammeter registers towards the high end of the scale and declines towards the zero end of the meter as the battery becomes more fully charged.

Battery Charge Rectifier
A component that changes AC voltage from the battery charge windings (within the STATOR) to DC voltage. This voltage could b used to charge a battery.

A conducting element, usually graphite and/or copper, which maintains sliding electrical contact between a stationary and a moving element.

The primary equation for calculating electrical power from mechanical horsepower is: HP=W/745. Where HP is horsepower, W is watts, and 745 is a conversion factor. We know from our previous discussion that power, in volt-amperes, is given by the following equation: P=I*V. For an inductive device like a motor, we also need to take into account the power factor (pf). Our equation for power becomes P=I*V*pf. The final equation then becomes: HP=I*V*pf/745.

Capacitor Run Electric Motor

Also referred to as air compressor motors these are very similar to capacitor start motors with one additional feature. These motors will also use a capacitor while the motor is running. These are most commonly found on applications such as air compressors where extra torque is necessary.

Capacitor Start Electric Motor
These motors will have one or more capacitors mounted to the motor that store electricity until it is turned on. The capacitor gives the motor an extra boost of electricity to reduce the starting current draw and increase starting torque.

Circuit Protection and Circuit Breakers
The purpose of the circuit breaker is to protect the wires between the breaker and the load, although it can also serve as a service disconnect (a means of disconnecting power from the circuit).
A wire or cable designed for the passage of electrical current.

A contactor is an electrically operated switch usually used in control circuits and whose contacts are considered high amperage compared to a relay.

This is found in universal and DC motors. These devices, along with the brushes serve to switch the polarity of the windings as the motor makes a revolution. (A forward and reversing switch, in short)

The laminations in the generator forming the magnetic structure.

The metal frame that surrounds and protects the generator/engine.

In short, current is the flow rate of electricity. It is interesting, though, how the term “current” is used both with respect to water and electricity. However, whereas water current is measured in units per minute passing through a damn or under a bridge or through a waterslide, electrical current is recorded by measuring the electrons per second are passing through a wire.

The flow of water through a pipe, or electrical current through a wire, is directly related to the pressure or voltage difference across the pipe or wire. Going back to the example of our two bath tubs: If you were to fill one tub with a couple of inches of water, the flow of water wouldn't be very fast filling the empty tub. If you then filled the second tub with several feet of water, the speed at which the water flowed out of the drain into the sewer would be much greater. The same is true with electricity--the greater the difference in voltage from one end of the wire to the other, the higher the current.

One complete reversal of alternating current of voltage, from zero to a positive maximum to zero to a negative maximum back to zero. The number of cycles per second is the frequency, expressed in Hertz (HZ).

Deep Cycle Battery Charger
A deep cycle battery supplies a relatively low amount of current for a long period of time. Deep cycle batteries, unlike car starting batteries, can be run down and recharged repeatedly with minimum loss of capacity.

Filler metal added during a welding operation.

A solid state device which allows current to pass in one direction only. Since it allows only one half cycle of an alternating current pass, its output will be unidirectional and it may be considered a rectifying element.

Direct Current (DC)
An electric current flows in one direction only. DC is produced by chemical action (i.e. a storage battery) or by electromagnetic induction.

A machine for converting mechanical energy into electrical energy by electromagnetic induction - a generator.

Regardless of the type of system, Efficiency is the difference between power in and power out. If you are peddling a bike, your legs are Power in, and the tire against the road is Power out. The difference between these two is the efficiency of power transmission.

For a bike, this loss of power, or efficiency, would be primarily the friction of the chain (even the friction of your shorts against your legs), wind resistance in the spokes, and even small frictional losses between the tire and the pavement, but it is not due to the steepness of the hill or wind resistance against you and the bike's frame, as this is a portion of the work the bike is performing (the load).
In a motor, the loss of power is due to the resistance of the windings, friction in the bearings, & air resistance inside the motor.

Electricity Types in Commercial Applications
There are three common terms used to describe the electricity used in commercial applications. Single-phase 120 volt, Single-phase 240 volt, and three-phase voltage (120/208, 120/240, or 277/480).
Don't be confused if you hear the terms 110 volts instead of 120 volts, or 220 volts instead of 240 volts. These are out of date terms people still refer to, but all public utilities in the US deliver 120 volts and 240 volts for consistency and load sharing. Most tools and motors use these other terms (110/220) just to indicate that they will still perform if the voltage drops to that level.
Any flowing electric current creates a magnetic field. When this current is flowing through a wire, the magnetic field forms circular rings around the wire. We can concentrate the magnetic field by coiling the wire into tight loops, thereby making an electromagnet.

We can concentrate the magnetic field even more, by wrapping the wire around an iron bar. This electromagnet also has both north and south poles like any other magnet, but the polarity of the poles changes as the electricity changes. If we send 60hz line power through an electromagnet, the polarity of the magnetic poles will alternate sixty times per second.

Electro-Motive Force (EMF)
The force causing current to flow in a conductor.

Engine Low Oil Shutdown
Will automatically shut engine down if oil level is insufficient for safe operation.

Engine Mechanical Governor
Throttles engine up to maintain RPM under load.

Four-Cycle or Four-Stroke Engine
Engine is lubricated by oil in the crankcase. Gas and oil are not mixed for fuel.

Friction Loss
The loss of pressure due to the resistance to flow in the pipe and fittings. Friction loss is influenced by pipe size and fluid velocity and is usually expressed in feet of head.

Full Pressure Lubrication Engine
Engine is lubricated by means of an oil pump located in the crankcase.

Full Power Outlet
Enables you to draw the full power of the generator out of one outlet.

Fully Automatic Battery Charger
The charger turns off automatically when the battery is fully charged. As the battery loses power the charger automatically turns back on.

A general name for a device that converts mechanical energy into electrical energy. The electrical energy may be direct current (DC) or alternating current (AC).

A connection, intentional or accidental, between an electrical circuit and the earth or some conduction body serving in the place of the earth. For example, the ground wire in your business or home is attached to an eight foot copper wire driven into the Earth an intended to keep your electrical devices and appliances from carrying current to you should they malfunction.

Idle Control
A system that controls the idle speed of the engine in direct relation to the electrical load.

Ignition Coil
A device used to supply DC voltage to the spark plugs.

If you have a magnet, and you are physically moving a wire near this magnet, it will create a current in the moving wire. The faster the wire is moved, the larger the current. Typically, the larger the magnet, the larger the current. If you change the direction the wire moves, the current will also change direction. This is the basic premise for a simple generator, where we use a diesel engine turn an armature moving wires past a magnetic field.

An inductive device is any coil of wire, which includes motors, transformers, and generators. Every time electricity flows through a wire, it creates a small magnetic field around the wire. (This is the same type of magnetism that holds a refrigerator magnet to the refrigerator, except that it is only present when current is flowing.) This magnetic field forms circular lines of flux around the wire. When we coil up a wire, we not only concentrate the wire itself into a small area, but we also concentrate the wire's magnetism into a small area too. An inductor stores energy in the magnetic field around the coils. It takes energy to develop the magnetic field around the coils, and the magnetic field gives off energy as it collapses (it collapses when the current is stopped or reversed.)

In an AC circuit, remember that the voltage is changing from positive, through zero, to negative 60 times every second. When we connect an inductor, like a motor or transformer, to an AC circuit, the magnetic field around the wires are also constantly changing as a result. They are continually expanding and contracting as the current is reversing.

Magnetic Poles
All magnets, regardless of type or origin, will have a north and south pole. This is very similar to a battery always having a positive and negative terminal. If you have two magnets, the poles with opposite polarity will attract one another, while poles with the same polarity repel one another. These attraction and repulsion forces can be quite strong, and this is what will make a motor turn.

An alternator with permanent magnets used to generate current for ignition in an internal combustion engine.

Neutral and Hot
The only difference between the Neutral wire and hot wire(s) of a modern electrical system is that the Neutral wire is forced to be at zero volts (anchored) by connecting it to Ground back at the circuit breaker panel.
If we did not anchor Neutral to Ground, then both the Neutral wire and the hot wire would be at some intermediate voltage (both would be free-floating). This is done as a safety issue. It is much easier to work on a system when we only have one wire with a non-zero voltage. Unlike the Ground wire however, the Neutral wire is designed to carry current during normal operation.

Ohms' Law
An Ohm is a unit of electrical resistance. One volt will cause a current of one flow through a resistance of one ohm.

In electrical systems, there is a relationship between current, voltage, and resistance. This is known as ohms law, and can be written in many different forms, but always boils down to V=IR, where V is voltage, I is current, and R is resistance.

This equation holds true whether we are dealing with AC, DC, Capacitive, Inductive, Three Phase, or any other type of circuit. However, it should be noted that sometimes the values for current and/or voltage are no longer simple values. The V and I of Ohms' Law can be replaced by complex mathematical expressions, but they still represent the current and voltage.
Ohm's law can be written in different forms, but are still the same equation. The three common forms of Ohms law are:
V=I *R

Parts of the Alternator
A motor is made up of electric and/or permanent magnets that are constantly attracting and/or repelling one another. This creates movement of the spinning rotor. The only thing that differs from one type of motor to another is how these magnets are created and controlled.

The uniform periodic change in amplitude or magnitude of an alternating current. Three phase alternating current consists of three different sine wave current consists of three different sine wave current flows, different in phase by 120 degrees from each other.

Power (in General)
For DC systems, power is the product of Current times Voltage, and will take on the form P=I*V. For AC systems with only resistive loads, the same holds true. But in capacitive or inductive circuits on an AC system, the device will momentarily store some power (or delay it), and so the issue becomes slightly more complicated. We need to compensate for this delay in power transmission, and this is where the term Power factor comes in.

Power Factor
When we us any capacitive or inductive device on an AC circuit, the current or voltage flowing through the circuit will be slightly delayed, or out of phase. A motor is an inductive element, and the current lags behind the voltage (remember, the inductor had the ability to store current). In a capacitor the voltage lags behind the current (the capacitor stores voltage). Due to the resistance inside the motor windings, a common power factor for electric motors is 0.8.

Power Transfer System
A system to safely wire your generator to your facility’s or home's electrical system, typically via an Automatic Transfer Switch.

Pressure and Voltage
The pressure in a pipe can be compared to electrical voltage across a wire. If the pressure on both ends of a pipe is the same, then no water will flow. If you took two water tanks of the same size, where one was full and the other was empty, and connected them together with a hose at their bottoms, water would flow from the full tank into the empty tank. The water would stop flowing when the depth of the water in each tank was the same.
The full tank has a higher pressure at the bottom (where the hose is connected) than the empty tank. When the depth of the water is equal in each tank, then the pressure at the bottom of both tanks is equal. If both ends of a wire are connected to the same voltage (for example, the positive terminal of a battery) then no current will flow either. In either case, it is the difference in pressure or voltage that causes the water or electricity to flow.
Rated Speed
The revolutions per minute at which the set is designed to operate.

Rated Voltage
The rated voltage of an engine generator set is the voltage at which it is designed to operate.

Real Power (Watts)
The real amount of power a device is using, or results in actual work performed, is called the "real power". Real power takes into account the fact that current or voltage is stored, or delayed. The real power tells us how much actual work can be performed, or how many horsepower our motor is delivering.
For a resistive and/or DC circuit, the apparent power and the real power are the same, but for a capacitive or inductive circuit, the real power is heavily dependent on the amount that the current or voltage is delayed. Real power is presented in Watts.

There is mathematically no difference between watts and volt-amperes, except that we use one term for apparent power, and one for real power, but they are both units of power. We use the power factor to go from apparent power to real power. The real power of a system is equal to the apparent power times the power factor. In every day use, this boils down to P=I*V*pf.

Rear Bearing Carrier
The casting housing the rotor bearing supporting the rotor shaft.

A device that converts AC to DC.

An electrically operated switch usually used in control circuits and whose contacts are considered low amperage, compared to a contactor.

Opposition to the flow of current. Changed by things like the size of the wire and the length of the wire, similar to water and a hose.

The rotating element of a generator.

Single Phase 120/240
Single phase 120 volt and 240 volt lines, are just different parts of the same system. This is actually a 240-volt system, but we split it in half to get two, 120-volt systems. This is the reason why it is called a single-phase system.
It is just one phase of power at 240 volts. To get the 120 volts, we use what is called a center-tap. Standard outlets use the Neutral wire (the center tap) and one hot wire, where the voltage between the Neutral and Hot is 120 volts. The 240 outlets use both hot wires, where one wire is 120 volts above the Neutral and the other is 120 volts below the Neutral (as before, we anchor the Neutral to Ground, and let the two Hot lines "float" above and below). It is said that each of the Hot legs (called poles) of a single-phase system are 180° out of phase. It can be confusing that this system is called single phase, but it might be helpful to refer to this as a two pole system. (Using the term two pole is correct, but calling it a two-phase system is incorrect.)

This is the stationary magnetic component in motors. On most motors, the stator's magnetic field is created from electromagnets, long coils of copper wires wound around this sheets of metal.

The rotor is the component that makes up the spinning shaft of the motor. It is almost always electromagnetic in nature (coils).

Single Phase
An AC load, or source of power normally having only two input terminals if a load or two output terminals if a source.

Tack Weld
A weld made to hold parts together in proper alignment until the final welds are made.

Tandem Trailer Axle
Refers to a trailer that has two axles instead of one allowing the trailer to carry additional weight.

A container for the storage of fluid in a fluid power system.

Three Phase Systems
Where the single-phase system has two poles 180° out of phase, the three phase system has three poles which are 120° out of phase (note 3*120° = 360° = full circle). Just as before, the voltage between the Hot and Neutral is 120 volts, but because of the phase angle, the voltage between any two Hot wires is 208 volts, which is 40*(0.866) = 208 volts. (Where 0.866 is the cosine of 120°.)

The majority of three phase motors don't use the Neutral wire. This is called a Delta Connected system. When the Neutral is used, it is called a wye-connected system. The majority of power sources are "wye- connected". A delta-connected load (motor) can always be connected to a wye source by just ignoring the Neutral wire, but the reverse is virtually never true. (It can be done, but it requires a center tap, three-phase, transformer to artificially create the Neutral.)

The company that is going to give 150% effort to help you every single time your call us.

Vibration Mount
A rubber device located between the engine or generator and the cradle to minimize vibration.

The unit of electromotive force. That electromotive force which when steadily applied to a conductor whose resistance is one ohm will produce a current of one ampere.

Electrical potential difference expressed in volts.

Voltage Regulator
A component that automatically maintains proper generator voltage by controlling the amount of DC excitation to the rotor.

Unit of electrical power. In DC terms, equal volts times amperes. In AC equals effective volts times effective amps times power factor times a consistent dependent on the number of phases. 1 kilowatt - 1,000 watts.

All the coils of a generator that make up the electromagnet that are wrapped around a laminated stack of iron sheets. Stator winding consists of a number stator coils and their interconnections. Rotor windings consist of all windings and connections on the rotor poles.