APFC-03 Reactive Power Compensation Method & Settings Presentation By: Tushar Mogre, CEO, Director. TAS PowerTek Pvt. Ltd. APFC-03 Reactive Power Compensation Method & Settings

APFC-03 PF correction Relay: Reactive Power Compensation Method & Settings. The APFC-03 PF correction relay has primary function of compensation of the reactive power for Power Factor compensation of the inductive loads by addition of right values of Capacitors in the supply system. It is used with the PF improvement system that is designed by usage of switched Capacitor banks. The bank sizing is decided by the system designer depending upon the Overall Capacitor compensation and minimum step size requirements. Thus, the settings on the APFC-03 are provided for the user to adjust it as per their application requirements. It is depending upon: Capacitor System Overall rating in terms of total KVAR of the system Overall Supply system rating in terms of KVA (Decided by the Nominal voltage feedback and CT primary rated current) The resolution of the Capacitor Panel. It is depending upon the steps sizing decided as per the application engineer for the Capacitor switching panel. Normally decided by the smallest Capacitor bank size. Requirement of the Target PF to be achieved within the acceptable tolerance range. This technical Note Presentation is for explaining the various settings that are required to be carried out by the Commissioning Engineer when the system is being commissioned.

Commissioning Engineer would therefore need to know following parameters before the APFC-03 is commissioned: Supply system Nominal Voltage – Phase to Phase Voltage (Or Phase to Neutral Voltage) value and supply frequency. Feedback Current CT primary rated current value in terms of Amp-AC-Fundamental. Capacitor Banks sizing of the system in terms of KVAR at supply system Nominal Voltage value. The parameters that would be set of APFC-03 that would affect the performance are: System Rated Supply Voltage CT Ratio PF Target : Inductive or Capacitive PF Target : Value of Target PF Steps Smallest KVAR safety factor Compensation Band Offset in % Rated Supply Voltage and CT ratio are the parameters that gets fixed once the supply system is installed on a specific supply and Current Transformers (CTs) are installed. PF Target is the requirement by the user for deciding the value of PF that can be set as per the supply system requirement. This too is normally fixed once the system pararmeter’s requirements are freezed. The capacitor bank sizing has to be carefully decided by the Application Engineer while designing the PF compensation system. But once the capacitor bank sizes are confirmed, commissioning engineer would be able to do small refinements on APFC-03 unit, in achieving the desired results for attaining the PF of the system.

As the Target PF is a specific value that is desired by the Electricity Consumers, the PF correction system step sizes decides the tolerance band around the set Target PF within which the PF can be maintained. For an example: If target PF is set at 0.980 inductive. If minimum capacitors has step size of 10KVAR @ rated supply voltage with overall PF panel capacity of 200KVAR @ 415V-ac. AND Rated Voltage of 415V (Ph-Ph) and CT primary current of 1000Amp. Presently, Load is having 3-ph Ph to Ph voltage of 420Vac with Current of 500Amp with Power Factor of 0.875 inductive. This means KW-Load = KVA-Load X PF-Load = (√3 X 420 X 500 / 1000) X 0.875 = 318.264 Then the exact requirement of KVAR compensation required is: KVAR-Target PF = KW-Load X [ tan{cos-1(PF-Load)} – tan{cos-1(PF-Target)} ] = 318.264 X { tan28.995 – tan11.478 } = 111.464 So, normalized voltage KVAR requirement is 111.464 X (415 / 420)2 = 108.826 KVAR. But the PF correction can either have 100KVAR OR 110KVAR that can be put in the system as the smallest capacitor bank size is 10KVAR. So, if 100KVAR is inserted, then 8.826KVAR (9.040KVAR at 420V) would remain uncompensated at rated voltage value And if 110KVAR is inserted, then 1.174KVAR (1.202KVAR at 420V) would be over-compensated at rated voltage value.

This also means that PF that can be achieved can rarely be of exact Target PF value but would be with some error. One has to know that PF-System Resolution (smallest step size normally decides resolution) would be the deciding factor for the error in PF compensation.

This can be depicted by KW – KVAR (X-Y) axis plot For achieving Target PF, the values of KVAR are KW & KVAR values of the load are Basic Power Plot When Capacitor banks, CT ratio & Target PF value is fixed Load KVA of the system is as shown by red arrow. With 100KVAR compensation With 110KVAR compensation This means that smallest Capacitor bank would decide the error in PF correction system. Load - KW Load KVAR - Inductive Load KVAR - Capacitive Maximum KVAR-ind Rating of PF system Maximum rated KVA value = √3 X (rated CT current) X (rated Voltage ph-ph) PF correction system Compensation range Area. 200KVAR 176.380 KVAR KVA for Target PF With 100 KVAR cap With 110 KVAR cap 318.264 KW 111.464 KVAR 64.916 KVAR 718.801 KVA Rated Apparent Power Value.

The Power Factor Correction Relay – APFC-03 is programmed to provide the right level of Capacitor banks compensation. But with the Accuracy of correction parameters decided by the following factors: Rated KVA of the supply system (decided by the CT rated current value & nominal rated voltage) Rating of the PF improvement system in terms of KVAR Resolution of the PF improvement system which is normally decided by the smallest capacitor bank size. So the user of PF-Correction controller APFC-03 has to understand that even though the target PF settings are programmed on it, the accuracy level of PF achieved would not be dependent upon the APFC-03, but it is dependent upon the above specified application engineering issues. Still, APFC-03 gives some options to adjust the PF compensation accuracy levels as per the User requirements. These are by adjustment of the parameters: Smallest KVAR safety factor Compensation Band Offset in %

APFC-03 PF correction relay (Or as a matter of fact any other make of PF regulation relay) may not be able to cater to the issues created by the system or application related issues. The PF correction panel designer has to look into various issues while deciding the Capacitor banking sizing, Panel KVAR capacity, type of switching arrangement along with speed of switching and supply system harmonics with system impedances distribution. For the detailed understanding on the subject matter, Application engineer is requested to go through the Book “Reactive Power Compensation on LV supply” by Tushar Mogre available as E-Book on www.amazon.com Further part of the this technical presentation would give the details on the adjustments and its implications on the PF correction along with accuracy of PF correction. It would also give the other relevant issues associated.

As it is well understood from the previous slides that accuracy of PF correction is primarily depending upon the “Regulation of the PF system”. That is the size of the smallest capacitor bank. Therefore, if the PF correction relay has a single point “Target PF” setting, it would never be able to see this exact value. It would go on turning ON and OFF the smallest capacitor bank during its every correction cycle time. In previous example, PF correction would keep the process on for switching ON and OFF the 10KVAR capacitor bank. This is because with capacitor bank OFF, the PF seen would be lower than the Target PF. AND with capacitor bank ON, the PF seen would be higher than the Target PF. To avoid this frequent switching ON and OFF of the smallest capacitor Bank, APFC-03 works on the principle of “NO ACTION KVAR BAND”. This means that there is a tolerance band created around the Target PF within which the PF is assumed to be fine by the APFC-03 and there would be NO switching ON or OFF of the capacitor banks. Only when the load changes its values, the KVAR requirement may go out of the said “NO ACTION KVAR BAND”. Then, APFC-03 would take the right corrective action to bring this within the said No Action Band by switching ON / OFF the capacitor banks.

CAPACITOR ADDITION BAND One can see the following KW – KVAR (X – Y axis) plot to see the “NO ACTION KVAR TOLERENCE BAND”. Load - KW Load KVAR - Inductive Load KVAR - Capacitive TARGET PF NO ACTION KVAR BAND CAPACITOR ADDITION BAND CAPACITOR REMOVAL BAND

NO ACTION KVAR BAND Compensation Band With 100% offset value The positioning of this “NO ACTION KVAR BAND” are the parameters that can be adjusted in APFC-03 by programming the parameter: Compensation Band Offset in % The values of this parameter can be adjusted from 0% to 100%. In can be understood from the plot here under: Load - KW Load KVAR - Inductive Load KVAR - Capacitive TARGET PF NO ACTION KVAR BAND Compensation Band With 100% offset value Compensation Band With 50% offset value Compensation Band With 0% offset value

Previous plot clearly shows the various positions of the “NO ACTION KVAR BAND” around the Target PF setting. This means that Error in achieving the Target PF is well defined within a specific tolerance band and positioning of this tolerance band around Target PF can be adjusted by the user of the system. Next is the width of the band around Target PF. Which is defined in APFC-03 parameter as Smallest KVAR safety factor. Load - KW Load KVAR - Inductive Load KVAR - Capacitive TARGET PF KVA Line NO ACTION KVAR BAND Smallest KVAR Safety Factor 1.9 ------ 1.1 This shows the effect of Value change in Smallest KVAR Safety Factor

The change in value of “Minimum KVAR safety factor” can determine the accuracy level of the given configured PF correction system. Smaller the value of this parameter, more accurate the PF correction system. Still, a very low value is programmed in this parameter, would cause frequent switching of “smallest capacitor bank” as well as even the other capacitor banks for smaller changes in load values. Very frequent switching of the capacitor banks can cause the “Maintenance Issues” and increase in the “Maintenance Costs” of the PF correction system. It can even reduce the operational reliability of the system and components like capacitors can experience the reduced life expectancy. Additionally, Power Quality issues of supply transients caused by capacitor switching too can be a matter of concern. In view of these points, the user has to decide the right value by taking into account all the issues with regards to accuracy of PF against the maintenance/PQ related issues. Any further clarification on APFC-03 functioning, please refer to the latest “User Manual”.

Thank You Presentation By: Tushar Mogre, CEO, Director. TAS PowerTek Pvt. Ltd.