Introduction to Power Quality
Lagging reactive power, primarily generated by inductive loads, is a significant cause of power and financial losses for electricity consumers, leading to a poor power factor (non-unity). Incorporating power factor correction (PFC) devices into the electrical network generates leading reactive power to compensate for lagging reactive power, helping consumers achieve a power factor close to unity (cos Ø ≈ 1).
This leading reactive power is typically supplied by Low Voltage (LV) capacitors connected in parallel to the supply network, situated close to the lagging power sources such as induction motors or MCC panels. These capacitors can be fixed for a given system load or variable in steps to adapt to changing load conditions.
Advantages of Power Factor Corrections:
- Reduction of reactive power in the system
- Lower energy costs due to improved power factor
- Improved voltage quality
- Reduced voltage drops
- Optimized cable design
- Reduced transmission losses
Figure 1: Power Triangle illustrates the relationship between Real Power (P), Reactive Power (Q), and Apparent Power (S). The formula Qc = PA · (tan Ø1 - tan Ø2) quantifies the reactive power compensation needed.
Figure 2: Typical Power Factor Correction Circuit Diagram shows a power factor correction system with filter circuit reactors for harmonic reduction. This system includes a PFC controller, fuses, capacitor contactors, reactors, and PFC capacitors connected to the load.
SIECAP™ LV Capacitors
Siemens SIECAP™ capacitors are designed to withstand high inrush currents, both during individual switching operations (>100IN) and when connected in parallel banks (up to 150IN). This high inrush is due to charging currents from the power line and other parallel capacitors.
The SIECAP™ range is classified into three variants:
- SIECAP™ ND [Normal Duty]
- SIECAP™ HD [Heavy Duty]
- SIECAP™ SHD [Super Heavy Duty]
Technology and Features:
- Based on MPP (Metalized Zinc Al alloy over Polypropylene dielectric) film technology.
- Impregnated with semi-dry biodegradable soft resin.
- Special film-cutting technique optimizes effective surface area for metal spraying.
- Compact and lightweight design.
- Self-healing properties: In case of electrical overload, the dielectric breaks down, creating plasma that isolates the faulty area within microseconds, resulting in negligible capacitance loss.
- Overpressure Disconnector: Activates at the end of service life or when internal pressure rises, safely disconnecting the capacitor from the line via an expansion bead.
- SIGUT Terminals: Provide finger touch protection (IP20) and ensure reliable connections.
Technical Specifications Summary:
| Feature | SIECAP™ SHD | SIECAP™ HD | SIECAP™ ND |
|---|---|---|---|
| Standards | IEC 60831-1/2 Edition 3.0 (2014), IS 13340-1/2 (2012) | ||
| Overvoltage | VN +10% (up to 8h daily), VN +15% (up to 30min daily), VN +20% (up to 5min daily), VN +30% (up to 1min daily) | ||
| Overcurrent (Imax) | Up to 1.3 ... 1.5·IN (A) | Up to 1.8·IN (A) | Up to 1.6 ... 2.0·IN (A) |
| Max. Inrush Current (Is) | ≤ 200 IN (A) | ≤ 250·IN (A) | ≤ 500 IN (A) |
| Losses (Dielectric) | 0.2 W/kvar | ≤ 0.2 W/kvar | 0.2 W/kvar |
| Losses (Total) | 0.45 W/kvar | ≤ 0.5 W/kvar | 0.45 W/kvar |
| Rated Frequency | 50/60* Hz | 50/60* Hz | |
| Capacitance Tolerance | -5/+10% | -5/+10% | -5%/+5% |
| Mean Life Expectancy | Up to 100,000 hours (-25/D) | Up to 130,000 hours (-25/D) | Up to 200,000 hours (-40/D) |
| Max. Switching Operations/Year | Max. 5,000 | Max. 7,500 | Max. 15,000 |
| Ambient Temperature | Class -25/D | Class -25/D | Class -40/60 |
| Max. Hotspot Temperature | 85 °C | 85 °C | 85 °C |
| Enclosure Degree of Protection | IP20 | IP20 | IP20 |
| Terminals | SIGUT | SIGUT | Fast-on or SIGUT |
Dimension Drawings: Detailed drawings are provided for Terminal Type A (fast-on) and Terminal Type B (Sigut terminals) for SIECAP™ ND and HD capacitors, and for Terminal Types A, B, C, D, E for SIECAP™ SHD capacitors, specifying dimensions like diameter (Ød), height (h), and terminal layout.
Detuned Reactors
Modern power electronics devices (drives, SMPS, UPS) introduce harmonics into the power supply, distorting the waveform. When capacitors are used for power factor correction, they can form a resonating circuit with the feeding transformer, typically at the 5th to 7th harmonic frequencies (250-500Hz). This resonance can lead to capacitor overloading, transformer/cable stress, voltage distortion, increased power losses, and nuisance tripping of protection equipment.
Detuned reactors are installed in series with capacitors to avoid resonance. They are designed so that the tuning frequency of the LC filter is lower than the dominant harmonic frequency. Above the tuning frequency, the combination acts inductively, providing a high impedance path to harmonics.
The detuning factor (p%) determines the tuning frequency (ft) using the formula: ft = fs / √(100/p), where fs is the supply frequency. For example, with a 7% detuned reactor and a 50Hz supply, the tuning frequency is approximately 189Hz, which is below the 5th harmonic (250Hz), thus preventing resonance.
Types Available:
- 7% Cu reactors
- 14% Cu reactors
- 5.67% Cu reactors
- 7% Al reactors
- 14% Al reactors
- 5.67% Al reactors
Technical Specifications Summary: Detailed tables provide specifications for various kVAr ratings, including De-tuning factor, Effective filter output, Rated voltage, Capacitance, Inductivity, Linear current, Effective current Irms, losses, weight, and dimensions for Cu and Al reactors.
APFC Controllers (7UG05 Series)
Siemens offers the 7UG05 series of Automatic Power Factor Controller Relays, designed for optimized power factor correction. These relays provide intelligent control and monitoring for power factor and power quality.
Key Features:
- Intelligent relay control (12 stages for 7UG0572, 8 stages for 7UG0571).
- Compliance with IEC 60947-5-1, CE, and RoHS standards.
- Dual-color backlight LCD display (7UG0572-1GT20, 7UG0571-1FT20) or 4-digit 7-segment LED display (7UG0572-1GT21).
- Universal control supply for variant optimization.
- Automatic, linear, or rotational switching of capacitor banks.
- Settable power factor range: 0.8 lag to 0.8 lead.
- Selectable 1A / 5A current input.
- Measurement and display of key parameters: Voltage, Current, Power factor, THDI, etc.
- RS485 Communication with MODBUS RTU Protocol.
Technical Data: Tables detail specifications such as display type, input ratings, environmental conditions, accuracy, measurement parameters, and connection details for different 7UG05 models.
Wiring and Dimensional Drawings: Diagrams illustrate wiring configurations (3-Phase 4-Wire, 1-Phase 2-Wire, 3-Phase 3-Wire, 2-Phase 2-Wire) and outline/panel cutout dimensions.
3TS Capacitor Duty Contactors
Siemens' 3TS Capacitor Duty Contactors are specifically designed for reliable and economical capacitor switching applications. With over 125 years of experience in industrial control products, Siemens offers high performance and improved reliability.
Key Features & Benefits:
- Range: 5kVAr - 50kVAr.
- Delatching operating principle for reliable switching (AC-6b utilization category).
- SIGUT Termination technique for finger touch proof terminals.
- Compact dimensions and flexible mounting (DIN/Screw).
- Ease of wiring, operator safety, and space saving.
- Designed to withstand permanent current (1.5x nominal) and high peak inrush currents.
Operating Principle: The contactors utilize a mechanical delatching mechanism. When energized, early-making auxiliary contacts connect the capacitor via damping resistors to attenuate inrush current peaks. Upon main contact closure, auxiliary contacts break. When de-energized, main contacts break the capacitive current.
Technical Specifications: Comprehensive tables detail specifications for various 3TS contactor types (3TS11, 3TS12, etc.), including dimensions, approvals, protection degrees, operational voltage and current, switching frequency, auxiliary contacts, and conductor connection details.
Selection and Ordering Data: Tables provide ordering codes for capacitor banks with AC coils, including built-in auxiliary contacts, and list spare parts, auxiliary contact blocks, and pre-charge resistor kits.
Selection Tables
The document includes several selection tables to aid in the proper specification of components for power factor correction systems:
- Standard Values: Selection Tables for Cables, Cable Cross Sections and Fuses: Provides recommended cable sizes (mm²) and fuse ratings (A) for various power (kVAR) ratings at different voltages (230V, 400V, 440V, 480V, 525V, 690V) and frequencies (50Hz, 60Hz).
- Calculation Table for Reactive Power Demand (Qc): Assists in calculating the required capacitor reactive power (Qc) based on motor power (kW), actual power factor (cos Ø), target power factor, and a factor (F) derived from tables.
- Individual PFC for Motors: Offers approximate capacitor power ratings (kVAR) for motors of different nominal ratings (kW) and speeds (r.p.m.). It also highlights the importance of correct sizing to avoid overvoltages.
- Individual PFC for Transformers: Provides standard values for capacitor power ratings (kVAR) for power factor correction of transformers (oil-immersed and cast resin), with a formula for exact calculation and a recommendation to consult power suppliers.
