Operating Alternators or AC Generators in Parallel

Pointers for Operating Alternators in Parallel:
1) If the load of a single generator becomes too large that its rating is exceeded, it is necessary to add another generator in parallel to increase the power available from the power station. Before attempting to connect AC generator in parallel, the following conditions must be met:

Three Phase Synchronous Motor

Figure 1: Cutaway view of  an eight pole, 2000 horsepower synchronous motor.

Introduction:
The synchronous motor is one type of three phase AC motor which operates at a constant speed from no-load to full-load.  It is similar in construction to a three phase AC generator but it has a revolving field which must be separately excited from a direct current source.  By changing the DC field excitation current, the power factor of this type of motor can be varied over a side range of lagging and leading values.  This motor is used in many industry applications because of its fixed speed from no-load to full-load, its high efficiency and to initial cost. It is also used to improve the power factor of three phase AC industrial circuits.

Polyphase Induction Motors

Figure 1: A typical three phase motor.

                                                     

Shaded Pole Induction Motor

Shaded-Pole Induction Motor

Figure 1: Cutaway view of a totally enclosed fan-cooled shaded-pole induction motor

A shaded-pole motor maybe defined as a single-phase induction motor provided with an auxiliary short-circuited winding or windings displaced in magnetic position from the main winding.

Shaded-pole induction motors are used in a wide variety of applications requiring an induction motor of 1/2 horsepower or less, even down to less than 1 mhp. It is simple in construction, low in cost, and extremely rugged and reliable - like a polyphase induction motor. Its torque characteristics and applications are similar to those of a permanent-split capacitor motor, except that it has a lower efficiency and a lower power factor. It is used in extremely wide variety of applications: home appliances, such as rotisseries, fans of all kinds such as those most commonly found in homes such as home electric fans, humidifiers, slide projectors; small business machines such as photocopy machines; vending machines, advertising displays, etc.

Electrical Control Circuit Schematic Diagram of Two-Value Capacitor Motor

TWO-VALUE CAPACITOR MOTOR

Figure 1: An autotransformer consisting of a coil of wire wound on a laminated core. The coil is tapped at several points to obtain different voltages

Electrical Control Circuit Schematic Diagram of Permanent Split Capacitor Motor

PERMANENT SPLIT CAPACITOR MOTOR

Figure 1: A permanent-split capacitor-run motor with the capacitor mounted on the motor

Electrical Control Circuit Schematic Diagram of Capacitor Start Motor

Figure 1: Typical capacitor start motor

Standard Terminal Markings of DC (Direct Current) Motors

Standard terminal markings, as developed by NEMA, are given for series, shunt and compound motors in figure 1, figure 2 and figure 3 respectively. These figures all show compensating-field as well as commutating-field windings since they are intended to cover both fractional horsepower and integral horsepower motors. Fractional horsepower motors do not generally use compensating windings and they may not use commutating-field (interpole) windings.

The markings are combinations of letters and arabic numerals, generally, these are as follows:

- Armature - A1, A2
- Control signal lead - C
- Series field - S1, S2
- Shunt field - F1, F2

Reversing DC Motors

Procedure for reversing direct current motors

Direct current motors are reversed by changing the direction of current flow through the armature or through the field. In series motors, the usual procedure is to reverse the current through the armature. Figure 1 shows this method.

All that is necessary is to interchange the leads on the brush holders. Figure 2 shows the series motor reversed by changing the current in the field circuits.

Commutating Field (Interpole) of DC Motors

Nearly all shunt and compound motors of 1/2 horsepower or more have commutating fields or interpoles located between the main poles. These interpoles have one winding of heavy wire and are connected in series with the armature as shown in figure 1. The purpose of the interpole is to prevent sparking.

Types of Direct Current (DC) Compound Motors

Figure 1: Two-pole compound DC motor

The motor shown in figure 1 above is one of the four different types of compound wound DC (direct current) motors. Although this type is known as the most common form of connection, it is the one used most often and the one which should be used unless otherwise specified. It is essential also to discuss the other types of compound wound DC motors.

Wiring Connection of Direct Current (DC) Motor

Connecting Direct Current (DC) Motors

It is of utmost importance to firstly know and understand the various internal configuration of the different types of DC motors before doing the actual wiring connection.  Although DC motors may appear to only have two leads for its external wiring connection terminals, it will serve best to habitually apply a good practice of knowing first the type of DC motor you are about to install before attempting any wiring connection and supplying power to run the motor.

Types of Direct Current (DC) Motors

Fundamental types of Direct Current (DC) motors:

1.) Series Field DC Motor - The series field DC motor contains field coils composed of a few turns of wire connected in series with the armature as shown in Figure 1 below.  This motor has high starting torque and a variable speed characteristic.  The greater the load the motor carries, the lower the speed.

Fundamental Overview of a DC Motor

Direct Current Motors - DC Motors are used to convert DC energy into mechanical energy. They are well suited for use as either constant-speed or adjustable speed motors. The three types (Shunt, Series, and Compound) which are available provide the range of speed torque characteristics for applications which require:

Warbling Alarm Circuit

The Warbling Alarm is made up of sawtooth wave generator and voltage controlled tone generator operated in tandem. Q1, R1, R2, C1, R3 comprise the sawtooth wave generator.

At the instant power is applied to the circuit, the voltage across C1 and hence at the anode of Q1 would be zero. C1 would then be slowly charged by R3 towards +12V. Once the voltage across C1 exceeds the value of the voltage appearing on the gate of Q1 as set by R1 and R2, the PUT (Programmable Unijunction Transistor) fires, that is, it will conduct, causing C1 to quickly discharge.Once C1 is discharged, Q1 will turn OFF, causing another charge - discharge cycle to be initiated. The manner in which the voltage across C1 varies, when plotted against time, resembles a sawtooth, hence the name sawtooth wave.

Inserting Alarm System to an Oil Pump Control Circuit

At some point in time, you may happen to have an old industrial pump unit wired inside an existing control panel that would require circuit modification in order to include an alarm system. What is being referred to here are pump systems most commonly found in industrial facilities such as oil pump, hydraulic pump, grease pump, water pump, air pump or air compressors, but nevertheless, the electrical circuit presented in this article may also be used to set an example to provide idea for other similar applications.

In heavy industrial facilities, one of the important foundation of a good working machinery is dependent on the condition of a well-oiled mechanism. This pertains to having a reliable lubrication system that ensures all moving parts of every machinery in the factory are well-lubricated in order to diminish friction and grinding on the machine's mechanical joints and contacts.

Electrical Circuit for Controlling a Lifting Electromagnet for Overhead Cranes with Top Running Trolley Hoist

When the need to conveniently pick up and lift heavy iron or steel objects for transferring from one place to another was seen as a necessity in heavy industrial facilities, the concept of using an electromagnet was implemented due to its ability to be turned ON and OFF which was then incorporated effectively to the hoist function of overhead cranes.

Overhead-travelling-crane magnets are electromagnetic device attached to the crane's hook to magnetically pick up heavy metallic loads for hoisting and transferring.  Cranes that are fitted with a lifting magnet are equipped with an electromagnet control circuit.

Wiring Connection for a Three Wire Solid State DC Proximity Sensor Without PLC

The previous article illustrated the concept of the wiring connection of a 3 wire DC proximity sensor to a PLC (Programmable Logic Controller). Alternatively, in this article, I will explain another approach on the wiring connection of the same proximity sensor but without using a PLC.

How to Connect a 3 Wire DC Solid State Proximity Sensor to a PLC

Knowing how to connect a 3 wire DC solid state proximity sensor to a PLC (Programmable Logic Controller) is dependent on the type of proximity sensor and the PLC to be used that is specific to the design of the circuit and the preferred application.

Pinch Roller Automatic Grip Control After Shear Cut Using PLC Program

What is a pinch roller? A pinch roller is a rotating machine consisting mainly of two rollers arranged in parallel either horizontally or vertically depending on the process required to pull the material that is rolled in the mill. These two rollers are coupled to a variable speed electric motor which is constantly rotating at a preset speed that is synchronized with the speed of the preceding finishing roller located before the pinch roller.