Estimating K Factor Loads
|For the most part, each designer or installer must make his/her own decision regarding what K-factor to assign to any load or load category. The following table is intended to assist in that determination by presenting what we believe are realistic, yet conservative, K-factors for a number of loads and load categories based on their relative harmonic producing capabilities.|
Calculating K Factor Loads
|1. List the KVA value for each load category to be supplied. Next, assign an ILK value that corresponds to the relative level of harmonics drawn by each type of load. See Table 2.
2. Multiply the KVA of each load times the ILK rating that corresponds to the assigned K-factor rating. This result is an indexed KVA-ILK value:
KVA x ILK=KVA -ILK
3. Tabulate the total connected load KVA for all load categories to be supplied.
|4. Next, add-up the KVA-ILK values for all loads or load categories to be supplied by the transformer.
5. Divide the grand total KVA-ILK value by the total KVA load to be supplied. This will give an average ILK for that combination of loads.
(Total KVA-ILK) ÷ (Total KVA) = average ILK
6. From Table 3, find the K-factor rating whose ILK is equal to or greater than the calculated ILK. Corresponding to this ILK is the K-factor of the transformer required.
Calculate the overall K-factor for several non-linear loads.
Load Category KVA Load x ILK = KVA-ILK Value
Discharge lighting 7.0 x 25.82 = 180.74
Receptacle circuits 2.0 x 123.54 = 247.08
Main frame computers 5.0 x 80.94 = 404.70
Motor w/drive 0.5 x 80.94 = 40.47
Motor w/o drive 1.5 x 0.00 = 0.00
Totals 16.0 872.99
Total KVA -ILK / Total KVA=average ILK
872.99/16 = 54.56 = average ILK
From Table 3, the nearest K-factor greater than or equal to the average ILK of 54.56 is K-13 with an ILK of 57.74.
Calculate the amount of additional K-30 load that can be handled by a 25KVA, K-13 transformer with 9KVA of spare capacity.
1. Determine the available spare K-13 KVA-ILK, using the ILK that corresponds to the transformer's K-factor rating.
spare KVA x ILK = spare KVA-ILK
9 x 57.74 = 519.66 spare KVA-ILK
2. Divide the spare KVA-ILK by the Index of Load K-rating for the load to be supplied.
The ILK for a K-30 load is 123.54
spare KVA-ILK / new load ILK @ K-30 =maximum additional KVA
519.66 / 123.54 = 4.2 KVA maximum additional KVA
3. Therefore, an additional 4.2 KVA of K-30 load could be added to this transformer. This additional loading represents the absolute maximum non-linear loading for that transformer.
For a transformer already partially loaded, any additional KVA loading must take into consideration the K-factor of each of the new loads to be added.