( aka active harmonic filter )
PART 1 - General
1.1 SUMMARY
This specification defines the electrical and mechanical characteristics and requirements for power correction systems in order to meet 5% total demand distortion [TDD], <5% total harmonic voltage distortion [THD(V)], and specific displacement power factor levels at selected points within the electrical system.
1.2 STANDARDS
The power correction systems shall be designed in accordance with the applicable sections of the following documents. Where a conflict arises between these documents and statements made herein, the statements made in this specification shall govern.
ANSI IEEE std C62.41-1991 [Surge Withstand Capacity]
CSA 22.2, No. 14 & 66 [CSA requirements for power electronics]
ANSI IEEE std 519-1992 [Harmonic limits]
UL 508C [UL requirements for power conversion equipment]
The products shall include third party approvals by UL or CSA.
1.3 SYSTEM DESCRIPTION
1.3.1 System Description
A. Voltage: 208 to 480 Volts, 380 to 600 Volts, 50/60 Hz, 3 phase, 3 wire plus ground.
B. Output Load Capacity: Rated capacity shall be the specified current capacity at the voltage required as indicated.
C. Field Installable Capacity Upgrade: Additional power correction capacity shall be added by installing additional units in parallel to previously installed power correction systems. A maximum of 5 units shall be installed in parallel per set of current transformers.
D. Current Transformers:
1. Split core type current transformers shall be installed as defined herein.
2. Two current transformers per power correction system location are required and mounted on phases A & B. C phase CT required when line-to-neutral loads present.
3. Current ratings of the current transformers shall be according to full load current of the circuit on which installed, 500, 1000, 3000, or 5000A to 5A secondary acceptable.
4. Current transformers rated for 400 hertz shall be used.
1.3.2 Modes of Operation
A. The power correction system shall be designed to electronically inject harmonic current to cancel the load produced harmonic current such that the upstream power harmonic current and voltage are reduced to below 5% TDD and 5% THD(V). TDD as used herein refers to the total load demand of the applied circuit. The applied circuit may be a single nonlinear load, an entire distribution-bus load, or the facility load at the point-of-common coupling (PCC) with the power source.
B. Reactive current compensation (aka displacement power factor correction) shall be activated via a digital keypad/display mounted on the door of the enclosure. When reactive current compensation is activated, the power correction system shall first perform harmonic current correction and then use the remaining capacity to inject reactive current compensation to the attain the specified level herein defined.
1.3.3 Performance Requirements
A. Input Power:
1. Voltage: automatically adapted to 208 - 480V, 380-600V, 3 phase plus ground
2. Voltage Tolerance: +/- 10% of nominal
3. Frequency: automatically adapted to 50 or 60 Hz, +/- 3 Hz
4. Surge Withstand Capability: ANSI/IEEE std C62.41-1991 without damage
5. Input Fuses: Rated at 200,000 AIC (amperes interrupting capacity), Class T
B. Output Performance
1. Performance of the power correction system shall be independent of the impedance of the power source. All performance levels shall be attained whether on the AC lines, backup generator, or output of UPS.
2. Harmonic Correction:
a. Limit the 2nd through 50th order harmonic current to <5% TDD at each installed location indicated herein. Harmonic levels for individual harmonic orders shall comply with respective levels established in ANSI/IEEE std 519-1992, Table 10.3.
b. Limit the THD(V) added to the electrical system immediately upstream of the power correction system location(s) to less than or equal to 5%. The power correction system shall not correct for utility supplied voltage distortion levels.
3. Reactive Current Compensation: to .95 lagging displacement power factor. Leading power factor is not permitted.
C. Current Transformers
1. Current transformers shall be rated for the total rated rms current of the total load at each installed location or higher.
2. Two (2) current transformers, mounted on phases A and B, are to be installed per location.
3. Each current transformer shall have a current output of 5 amperes. Current capacity of each current transformer shall be 5000, 3000, 1000 or 500 Ampere primary as required for the electrical system where installed. No other ratings are acceptable.
4. Each current transformer shall be rated for 400 Hertz.
1.4 ENVIRONMENTAL CONDITIONS
The power correction system shall be able to withstand the following environmental conditions without damage or degradation of operating characteristics or life.
1. Operating Ambient Temperature: 00C (320F) to 400C (1040F).
2. Storage Temperature: -400C (-400F) to 650C (1490F).
3. Relative Humidity: 0 to 95%, non-condensing.
4. Altitude: Operating to 1000 meters (3300 ft). De-rated for higher elevations.
5. Audible Noise: Generated by power correction system not to exceed 65 db measured at 1 meter from surface of unit.
PART 2 - PRODUCT
2.1 ENCLOSURE
A. Each power correction unit shall be provided in an IP-20 (aka NEMA 1) rated enclosure.
B. Chassis units are installed into the switchgear and MCC.
C. Units rated 100 Amperes and under for total output current shall be designed for wall mounting with cable entry through the bottom. Units rated greater than 100 Amperes for total output current shall be freestanding for floor mounting and top cable entry.
D. When indicated in the electrical-mechanical drawings, the power correction system shall be mounted in the motor control centers or power distribution panels.
E. Freestanding units shall include a door-interlocked disconnect that provides power interruption when the door is opened. Disconnect shall be lockable in the power-off position. Wall mount units shall be disconnected from the power source by a disconnect device or circuit breaker contained in the power distribution center as defined by local and national codes for branch circuit protection.
F. Freestanding units shall include lifting provisions by forklift truck and lifting lugs. Wall mount units weighing more than 80 pounds shall have lifting lugs.
G. All units shall include 200,000 AIC rated fuses with Class T actuation.
H. All units shall be provided with a grounding lug. Grounding by the contractor is to be performed according to local and national standards.
I. The paint shall be the manufacturer’s standard type and color.
2.2 OPERATOR CONTROLS and INTERFACE
A. All units shall include a digital interface model (DIM) that includes an alphanumeric display consisting of 2-lines with 20 characters per line. All information shall be in English. Display shall be easily viewed under all lighting conditions, including sunlight, as found inside buildings.
B. Operators include run, stop, setup, enter, and up/down scroll.
C. The display shall provide operating data while functioning. Standard operating parameters available for display are AC line voltage, total rms load current, harmonic current of load, reactive current of load, output harmonic and reactive current of power correction system.
D. When the output of the power correction unit is at full rated capacity, the display shall indicate at-maximum capacity and actuate an at-maximum capacity relay.
E. All fault conditions shall be displayed as they occur. Diagnostic information shall be provided in English and clearly indicate the nature of the fault.
F. The run pushbutton shall include a green LED. LED shall be lighted when unit is operating.
G. Contacts shall be provided for operator information for power-on, run, fault and at-maximum capacity. Each contact shall be rated for 1 Ampere at 120/240 volts. One form C contact shall be provided for each relay.
H. A RS485 serial communication port shall be provided for remote control and diagnostic information.
2.3 DESIGN
A. All power correction units shall be defined as a power electronic device consisting of power semiconductors that switch into the AC lines to modulate its output to cancel detrimental harmonic and/or reactive currents. A DC bus shall store power for power semiconductor switching. A microprocessor shall control the operation of the power converter.
B. Each unit shall be designed with a current limiting function to protect the semiconductors. When this level is attained, a message shall be displayed indicating the output capacity is at-maximum capacity and actuate the at-maximum capacity relay. Operation shall continue indefinitely at this level without trip off or destruction of the power correction unit.
C. Each unit shall incorporate an over-temperature output roll back that reduces the total output current in order to maintain maximum current correction within the electrical system.
D. Two distinct levels of faults shall be employed. Non-critical level faults will provide automatic restart and a return to normal operation upon automatic fault clearance. Critical level faults stop the function of the unit and await operator action.
1. Faults such as AC line over voltage, AC line under-voltage, AC line power loss, and AC line phase imbalance shall be automatically restarted. Upon removal of these fault conditions, the power correction system shall restart without user action. Automatic restart will not occur if 5 faults have occurred in less than 5 minutes. During the fault condition, except line loss, the display shall state the type of fault and indicate that automatic restart will occur. The run relay and run LED shall be disabled. The fault relay shall not be enabled unless time out occurs. Upon AC line loss, the power-on relay shall be disabled and no display shall be provided.
2. All other types of faults shall be considered critical and stop the power correction system. The display shall indicate the fault condition and “stop.” The run LED and relay shall be disabled and the fault relay enabled. User shall be required to initiate a power reset (turn power off and on) to restart the power correction system.
E. The logic of the power correction system shall monitor the load current by utilizing two (2) current transformers (CTs) mounted on phases A and B to direct the function of the power electronic converter. The ratio of the CTs must be entered into the logic via the digital keypad/display to calibrate the operation of the power correction system. The output of the current transformers shall be 5 Amperes.
F. Up to 5 power correction units may be installed in parallel to inject current according to the information received from one set of CTs. The units will function independently. If one unit is stopped or faulted, the remaining units will adjust accordingly to maintain optimum harmonic cancellation levels up to the capacity of the remaining units.
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