Quiz 1

• A transformer is a stationary machine of high efficiency by means of which AC power may be changed from one voltage to another without changing its frequency.
• A transformer is a simple and efficient machine that changes the level of energy from high voltage to low voltage and vice versa.
• Unlike in rotating machines, there is no electrical to mechanical energy conversion in transformers.
• Transformers are usually better than 98.5 percent efficient.
• Transformers have no moving parts.
• Transformers transfer electric power from one circuit to another magnetically.
• The transfer enables changes to be made in the voltage (and current) output.
• Transformers enabled the development of economically feasible ac systems.
• A transformer consists of a core made up of laminated sheets of iron which interlinks two coils of insulated wire placed upon it.
• The primary winding of the transformer is connected to the high voltage or high current circuit, and the meter or relay is connected to the secondary circuit.
• A power transformer is a big transformer installed in power plants and central substations.
• A step-up transformer has more turns of wire on the secondary coil, which makes a larger induced voltage in the secondary coil.
• The most common usage of an instrument transformer is to operate instruments or metering from high voltage or high current circuits.
• A power transformer must be designed with high efficiency at rated capacity.
• A step-down transformer has less turns of wire on the secondary coil, which makes a smaller induced voltage in the secondary coil.
• A distribution transformer is designed for high efficiency all day operation.
• A power transformer is very widely used for stepping up and stepping down the voltage at the electrical power generating station and distribution station (or substation) respectively.
• An ideal transformer has no losses and no leakage flux.
• The primary winding of a transformer is the winding that is connected to an AC power source of suitable voltage.
• The secondary winding of a transformer is the winding that is connected to the load.
• A transformer operates on the principle of mutual inductance between two inductively coupled coils.
• A transformer consists of two windings in close proximity and are coupled by magnetic induction.
• One of the windings in a transformer, called primary, is energized by a sinusoidal voltage.
• The secondary winding of a transformer feeds the load.
• The alternating current in the primary winding sets up an alternating flux in the core of a transformer.
• R 01 X 01 E 1 E 2 LOA D I 1 I 2 V 2 is the equivalent circuit referred to the secondary side.
• 𝑍 02 = 𝑅 02 2 + 𝑋 02 2 is the equivalent impedance referred to the secondary side.
• 𝑅 01 = 𝑅 1 + 𝑎 2 𝑅 2 is the equivalent resistance referred to the primary side.
• 𝑍 01 = 𝑅 01 2 + 𝑋 01 2 is the equivalent impedance referred to the primary side.
• 𝑅 02 = �� 2 + �� 1 𝑎 2 is the equivalent resistance referred to the secondary side.
• 𝑋 02 = 𝑋 2 + 𝑋 1 𝑎 2 is the equivalent reactance referred to the secondary side.
• R 1 X 1 E 1 E 2 LOA D I 1 I 2 V 2 R 2 X 2 V 1 is the equivalent circuit referred to the primary side.
• 𝑋 01 = 𝑋 1 + 𝑎 2 𝑋 2 is the equivalent reactance referred to the primary side.
• The secondary winding of a transformer is linked by most of this flux and emfs are induced in the two windings.
• If 120 V is impressed across the H 1 and H 2 terminals of a 2300/230 V distribution transformer, the voltmeter reading will be 12 V if the polarity is additive and 108 V if the polarity is subtractive.
• Proper transformer polarity is needed when transformers are connected in parallel or when transformers are banked.
• The polarity of a transformer refers to the relative directions of the induced voltage in the primary and secondary windings with respect to the manner in which the terminal leads are brought out.
• The impedance referred to the high side in a circuit is represented as 𝑅 0𝐻 = 𝑃 𝑠𝑐 �� ���� 2 = 42
• The resistance, reactance and impedance referred to the high side can be calculated using the equivalent circuit.
• The emf induced in the secondary winding of a transformer drives a current through the load connected to the winding.