Technical description
In an electricity system the reactive power industry influences the quality deterioration of the energy network parameters and the increase of electricity charges. The ZPUE S.A. company has in its offer solutions for compensation of the inductive and capacitive reactive power, such as:
- capacitor banks,
- capacitor banks with protective chokes,
- capacitor banks (to be agreed upon with the manufacturer, after completing an analysis of the energy network parameters of the facility).
Reactive power compensation in electricity system
There are three distinguished stages of reactive power compensation:
- Central compensation
The capacitor bank is installed on the main switchgear (the most frequent application). - Group compensation
The capacitor bank is installed on the subswitchgear or near the group of recipients (in extensive cable network, dispersed recipients). - Individual compensation
Capacitors installed on single recipients (high power recipients).
| Capacitor banks technical data: | |
| Rated power | from 40 up to 600 kvar 1) |
| Rated power of the increment | from 5 up to 60 kvar |
| Number of compensation levels | from 4 up to 15 |
| Capacitor bank operation rated voltage | 400 V 2) |
| Isolation rated voltage | 690 V 3) |
| Power frequency | 50 (60) Hz |
| Busbar rated short-time withstand current | up to 40 kA |
| Protection degree | IP3X 4) |
| Cooperation with current transformers | xx/5 |
| Power supply | from the top or from the bottom |
Notice:
1) Possibility to connect together capacitor banks to bigger sets.
2) Possibility to manufacture 500 V and 690 V capacitor banks.
3) 690 V capacitor bank requires 750 V isolation.
4) Possibility to manufacture up to IP54 protection degree.
General principles of capacitor bank selection
The role of the reactive power in total power consumption is determined by two coefficients. The first is the power coefficient cosφ, which was presented in relation/ratio (1.1)
When the cosφ is closer to one, the role of the reactive power is smaller. Energy suppliers usually use the power coefficient tgφ in their settlement contracts. A power coefficient tgφ was received from the relation/ratio(1.2)
When the tgφ is closer to 0, the supply of the reactive power is smaller. On the basis of received tgφ and required active power,the indicative power of the capacitor bankscan be calculated. The QBat capacitor banks’ power is determined from the relation/ratio (1.3)
tgφ corresponds to – power coefficient required by the power plant.
Power and energy chart
| P - active power [kW] |
| Ea - active energy [kWh] |
| Q - reactive power [kvar] |
| Er - reactive energy [kvarh] |
| S - apparent power [kVA] |
| Eopp - apparent energy [kvah] |
Notice!
In order to select capacitor banks properly, it is necessary to meter the electricity network in the facility.
Capacitor bank protection against adverse effects of higher harmonics
Applying rectifiers, power inverters and frequency inverters to modern receiving devices is very often the main cause of voltage and current deformation, which results in a change in their sinusoidal waveform. They include numerous harmonics , which are an undesirable phenomenon, because they reduce the lifetime of the electrical devices. This phenomenon is particularly dangerous in relation to the capacitor bank. A condenser reactance is reduced when the frequency is higher. In consequence, a high voltage current flows through the capacitor and causes damage. In order to protect the capacitor banks against the adverse effects of higher harmonics, protection chokes connected in series with capacitors are used.
The level of disturbance present in the network (the number of harmonics) is defined by THD coefficient. Depending on the THD coefficient, the capacitor bank type is chosen.
| THD ≤ 15% | Capacitor bank with normal capacitors (Un Kond = 400 V) |
| 15% ≤ THD ≤ 25% | Capacitor bank with reinforced capacitor banks (Un Kond = 440 V) |
| 25% ≤ THD ≤ 50% | Capacitor bank with compensation chokes |
| THD > 50% | Tracking compensator based on semiconductor elements |
Capacitor banks manufactured by ZPUE S.A. are identified by the bank type symbol and cubicle type
| Capacitor bank type: | |
| BI | Inductive capacitor bank |
| BK | Typical capacitor bank (Un Kond = 400V) |
| BKW | Reinforced capacitor bank (Un Kond = 440V) |
| BKD7 | Capacitor bank with chokes 7% |
| BKD14 | Capacitor bank with chokes 14% |
| Cubicle type: | |
| R | Cubicle type RN-W |
| I | Cubicle type INSTAL-BLOK |
| Z | Cubicle type ZR-W |
