ENERGY SAVING BALLAST BASIC INFORMATION AND TUTORIALS

The market for magnetic (core and coil) ballasts is shrinking! The National Appliance Energy Conservation Amendment of 1988, Public Law 100-357 prohibited manufacturers from producing ballasts having a power factor of less than 90%.

Ballasts that meet or exceed the federal standards for energy savings are marked with a letter “E” in a circle. Dimming ballasts and ballasts designed specifically for residential use were exempted.

Today’s electronic ballasts are much lighter in weight and considerably more energy efficient than older style magnetic ballasts (core and coil). Energy saving ballasts might cost more initially, but the payback is in the energy consumption saving over time.

Old-style fluorescent ballasts get very warm and might consume 14 to 16 watts, whereas an electronic ballast might consume 8 to 10 watts. Combined with energy-saving fluorescent lamps that use 32 or 34 watts instead of 40 watts, energy savings are considerable. You are buying light, not heat.

When installing fluorescent luminaires, check the label on the ballast that shows the actual volt amperes that the ballast and lamp will draw in combination. Do not attempt to use lamp wattage only when making load calculations because this could lead to an overloaded branch circuit.

For example, a high-efficiency ballast might draw a total of 42 volt-amperes, whereas an old-style magnetic ballast might draw 102 voltamperes.

The higher the power factor rating of a ballast, the more energy efficient. Look for a power factor rating in the mid to high 90s.

Various line currents, volt-amperes, wattages, and overall power factor for various single-lamp

fluorescent ballasts.

Ballast Line Current Line Voltage Line Volt-Amperes Lamp Wattage Line Power Factor

No. 1   0.35                120                              42                    40                    0.95(95%)

No. 2   0.45                120                              54                    40                    0.74(74%)

No. 3   0.55                120                              66                    40                    0.61(61%)

No. 4   0.85                120                              102                  40                    0.39(39%)

No. 5   0.22                120/277                       26                    30                    0.99(99%)

CAPACITOR INSTALLATION SYSTEMS BENEFITS BASIC INFORMATION AND TUTORIALS

What Are The Benefits Of Installing Capacitors?

Power capacitors provide several benefits to power systems. Among these include power factor correction, system voltage support, increased system capacity, reduction of power system losses, reactive power support, and power oscillation damping.

Power Factor Correction.

In general, the efficiency of power generation, transmission, and distribution equipment is improved when it is operated near unity power factor. The least expensive way to achieve near unity power factor is with the application of capacitors.

Capacitors provide a static source of leading reactive current and can be installed close to the load. Thus, the maximum efficiency may be realized by reducing the magnetizing (lagging) current requirements throughout the system.

System Voltage Support.

Power systems are predominately inductive in nature and during peak load conditions or during system contingencies there can be a significant voltage drop between the voltage source and the load. Application of capacitors to a power system results in a voltage increase back to the voltage source, and also past the application point of the capacitors in a radial system.

The actual percentage increase of the system voltage is dependent upon the inductive reactance of the system at the point of application of the capacitors. The short-circuit impedance at that point is approximately the same as the inductive reactance; therefore, the 3-phase short-circuit current at that location can be used to determine the approximate voltage rise.

Increased System Capacity.

The application of shunt or series capacitors can affect the power system capacity. Application of shunt capacitors reduces the inductive reactive current on the power system, and thus reduces the system kVA loading. This can have the effect of increasing system to serve additional load.

Series capacitors are typically used to increase the power carrying capability of transmission lines. Series capacitors insert a voltage in series with the transmission line that is opposite in polarity to the voltage drop across the line, which decreases the apparent reactance and increases the power transfer capability of the line.

Power System Loss Reduction.

The installation of capacitors can reduce the current flow in a power system. Since losses are proportional to the square of the current, a reduction in current will lead to reduced system losses.

Reactive Power Support.

Capacitors can help support steady-state stability limits and reactive power requirements at generators.

Power Oscillation Damping.

Controlled series capacitors can provide an active damping for power oscillations that many large power systems experience. They can also provide support after significant disturbances to the power system and allow the system to remain in synchronous operation.

POWER FACTOR IN AC MACHINES BASIC AND TUTORIALS

The power factor at which ac machines operate is an economically important feature because of the cost of reactive kilovoltamperes. Low power factor adversely affects system operation in three principal ways.

(1) Generators, transformers, and transmission equipment are rated in terms of kVA rather than Kw because their losses and heating are very nearly determined by voltage and current regardless of power factor.

The physical size and cost of ac apparatus are roughly proportional to kVA rating. The investment in generators, transformers, and transmission equipment for supplying a given useful amount of active power therefore is roughly inversely proportional to the power factor.

(2) Low power factor means more current and greater 12 R losses in the generating and transmitting equipment.

(3) A further disadvantage is poor voltage regulation.

Factors influencing reactive-kVA requirements in motors can be visualized readily in terms of the relationship of these requirements to the establishment of magnetic flux. As in any electromagnetic device, the resultant flux necessary for motor operation must be established by a magnetizing component of current.

It makes no difference either in the magnetic circuit or in the fundamental energy conversion process whether this magnetizing current be carried by the rotor or stator winding, just as it makes no basic difference in a transformer which winding carries the exciting current. In some cases, part of it is supplied from each winding.

If all or part of the magnetizing current is supplied by an ac winding, the input to that winding must include lagging reactive kVA, because magnetizing current lags voltage drop by 90 °. In effect, the lagging reactive kVA set up flux in the motor.

The only possible source of excitation in an induction motor is the stator input. The induction motor therefore must operate at a lagging power factor. This power factor is very low at no load and increases to about 85 to 90 percent at full load, the improvement being caused by the increased real-power requirements with increasing load.

With a synchronous motor, there are two possible sources of excitation: alternating current in the armature or direct current in the field winding. If the field current is just sufficient to supply the necessary mmf, no magnetizing-current component or reactive kVA are needed in the armature and the motor operates at unity power factor.

If the field current is less, i.e., the motor is underexcited, the deficit in mmf must be made up by the armature and the motor operates at a lagging power factor. If the field current is greater, i.e., the motor is overexcited, the excess mmf must be counterbalanced in the armature and a leading component of current is present; the motor then operates at a leading power factor.

Because magnetizing current must be supplied to inductive loads such as transformers and induction motors, the ability of overexcited synchronous motors to supply lagging current is a highly desirable feature which may have considerable economic importance. In effect, overexcited synchronous motors act as generators of lagging reactive kilovoltamperes and thereby relieve the power source of the necessity for supplying this component.

They thus may perform the same function as a local capacitor installation. Sometimes unloaded synchronous machines are installed in power systems solely for power-factor correction or for control of reactive-kVA flow. Such machines, called synchronous condensers, may be more economical in the larger sizes than static capacitors.

Both synchronous and induction machines may become self-excited when a sufficiently heavy capacitive load is present in their stator circuits. The capacitive current then furnishes the excitation and may cause serious overvoltage or excessive transient torques.

Because of the inherent capacitance of transmission lines, the problem may arise when synchronous generators are energizing long unloaded or lightly loaded lines. The use of shunt reactors at the sending end of the line to compensate the capacitive current is sometimes necessary.

For induction motors, it is normal practice to avoid self-excitation by limiting the size of any parallel capacitor when the motor and capacitor are switched as a unit.

POWER FACTOR CORRECTION USING SYNCHRONOUS MOTORS BASIC INFORMATION

Synchronous motors were first used because they were capable of raising the power factor of systems having large induction-motor loads. Now they are also used because they can maintain the terminal voltage on a weak system (high source impedance), they have lower cost, and they are more efficient than corresponding induction motors, particularly the low-speed motors.

Synchronous motors are built for operation at pf = 1.0, or pf = 0.8 lead, the latter being higher in cost and slightly less efficient at full load. The selection of a synchronous motor to correct an existing factor is merely a matter of bookkeeping of active and reactive power.

The synchronous motor can be selected to correct the overall power factor to a given value, in which case it must also be large enough to accomplish its motoring functions; or it can be selected for its motoring function and required to provide the maximum correction that it can when operating at pf = 0.8 lead.

In Fig. 20-8, a power diagram shows how the active and reactive power components Ps and Qs of the synchronous motor are added to the components Pi and Qi of an induction motor to obtain the total Pt and Qt components, the kVAt, and the power factor.

The Qs of the synchronous motor is based on the rated kVA and pf = 0.8 lead, rather than the actual operating Kva. The synchronous motor can support the voltage of a weak system, so that a larger rating synchronous motor can be installed than an induction motor for the same source impedance.

With an induction motor, both the P and Q components produce voltage drops in the source impedance. With a synchronous motor operating at leading power factor, the P component produces a voltage drop in the source resistance, but the Q component produces a voltage rise in the source reactance that can offset the drop and allow the terminal voltage to be normal.

If necessary, the field current of the synchronous motor can be controlled by a voltage regulator connected to the motor bus. The leading current of a synchronous motor is able to develop a sufficient voltage rise through the source reactance to overcome the voltage drop and maintain the motor voltage equal to the source voltage.

FIGURE 20-8 Power diagram of induction motor and synchronous motor operating in parallel, showing component and net values of P and Q.