Reactors and Isolation Transformers

Question 1

What is a Reactor

Answer 1

-Limit inrush current and reduce notching.
= Is a coil added in SERIES WITH THE LOAD to reduce inrush current, voltage notching and voltage spikes.
-Rated by the ohms of impedance that they provide at a given frequency and current.
-Dry type or Oil immersed.

Question 2

Two Types of Reactors

Answer 2

-Dry Type = common for low voltage applications.
-Oil-immersed = common in high voltage applications.

Question 3

Two Types of Power Quality Problems

Answer 3

1 Rectifiers -Nonlinear rectified power supply
2 Drive induced ground currents

Question 4

Rectifiers

Answer 4

Motor Drives rectify incoming power to form a DC voltage.
-SMPS switched mode power supply
-IGBT insulated gate bipolar transistor
-SCR silicon controlled rectifier

Question 5

SCR

Answer 5

Used as a switch where a small triggering current controls the flow of a larger current.
-Can cause notching, due to transient short circuits flowing when more than one SCR is ON.

Question 6

Notches

Answer 6

Is a distortion in a voltage waveform where the voltage quickly drops toward zero and then returns to the correct value.
-The number of notches in a cycle is equal tot eh number of rectifiers or pulses in the power supply.

Question 7

Zero Crossovers

Answer 7

Used for timing signals, such as clocks and alarms.

Question 8

Common-Mode Noise

Answer 8

Is a type of electromagnetic interference induced on the power or communication line.

Question 9

Line Input Reactors

Answer 9

Used when LOW Line Impedance allows High inrush current, when power factor correction capacitors are used or when a motor drive causes notching.

Question 10

Load Output Reactors

Answer 10

Are installed at the output of a motor drive.
Help eliminate voltage spikes or reflected wave noise by slowing down the rate of change in the drive output voltage.

Question 11

Saturable-Core Reactor

Answer 11

Is an inductor whose inductance is controlled through the use of a magnetic field created by a second winding wound around the same iron core as the primary winding.

Question 12

Choke

Answer 12

is a reactor used to restrict the current to AC or DC drives in the case of short circuits in the drive itself.
-builds CEMF when large short circuit currents are drawn from the source. This reduces the available voltage to the drive. This causes the instantaneous electronic trip circuit to trip the drive off line.

Question 13

Common mode choke

Answer 13

a reactor used to reduce common mode noise current generated by the rapid switching of a motor drive or signaling device.
-uses two windings. One winding to the load, and one away from the load. The resulting two opposite magnetomotive forces cancel and result in zero inductance. Any additional current such as common mode noise, the imbalance results in a magnetomotive force that opposes the flow of the noise current. Load current is unimpeded while blocking the noise current.

Question 14

Resonance

Question 15

Isolation Transformers

Answer 15

Act as a buffer between a nonlinear power supply, the load, and the power source.
-Used to provide cleaner power to nonlinear loads and to prevent harmonics from moving upstream into the power source.

Question 16

Drive Isolation Transformer

Answer 16

Placed between the system supply power and the electronic motor drive.
1)Voltage Change
2)Reduction of drive induced ground currents
3)Reduction of common mode noise

Question 17

Drive Isolation Transformer General Equipment Applications

Answer 17

1 SCR controlled heating of furnaces
2 3-phase rectifier input DC power Supplies
3 3-phase switched mode power supplies

Question 18

Three Benefits to grounding the Secondary

Answer 18

1 Superior transient and impulse immunity to the load side of the transformer
2 Reduces common mode noise coupling from primary to secondary
3 Prevents induced ground current from transferring upstream into the primary system.

Question 19

Electrostatic Shields

Answer 19

Can prevent common mode noise from transferring from the transformer’s primary to the secondary ONLY if the secondary is UNGROUNDED.