Sonel PQM analyzers case study #12: Reactive power charges

Non-linear load points such as UPSs, computer power supplies, LED lighting, inverters, air conditioners, etc. draw distorted current from the mains. One of the negative effects of such operation is the generation of capacitive reactive power into the grid. Electricity suppliers usually do not allow this to happen and charge additional fees that are actually penalties, often significant ones.

Description of the identified problem

A company producing electronic devices incurred additional charges worth several thousand PLN per year due to the generation of capacitive reactive power. It is necessary to diagnose the problem and possibilities of reactive power compensation.

Measurement tools used

• Sonel PQM-710 analyser
• Set of F-3A clamps (In=3000 A)
• Sonel Analysis software

 

Figure 1 Weekly graph of three-phase reactive power before compensation

 

Figure 2 Weekly graph of reactive power in individual phases

 

Figure 3 Weekly graph of three-phase reactive power (inductive, capacitive)

 

PRELIMINARY CONCLUSIONS:

1. After analysing the data over a period of one week, one can note a cyclical variation of reactive power from inductive to capacitive and vice versa (change of power sign in Fig. 1). The electronic power meter counts both types of energy independently in the corresponding registers.
2. Generation of capacitive reactive power is subject to charges (Fig. 3).
3. Despite the consumption of inductive reactive power, no additional charges were incurred on this account.
4. Due to the non-uniform loading of the phases with single-phase loads (Fig. 2), a dynamic compensator was selected for improvement, which additionally allows other network parameters to be improved.

After the dynamic compensator was installed and put into operation, measurements were taken again over a period of one week. The recorded data clearly indicate capacitive reactive power compensation. In Fig. 4, the reactive power waveform can be observed to be inductive, with no change to capacitive, translating into zero capacitive reactive power (Fig. 5.).

 

Figure 4 Weekly graph of three-phase reactive power after compensation

 

Figure 5 Weekly graph of three-phase reactive power after compensation (inductive, capacitive)

 

Since only inductive reactive power is present in the network after compensation, the tg(φ) factor was checked, which must not exceed the value of 0.4 under the Polish regulations. Fig. 6 shows that the factor is below this value.

 

Fig. 6. Distribution of the tg(φ) factor over a period of one week

 

FINAL CONCLUSIONS:

1. With the use of a dynamic compensator, the generation of capacitive reactive power was completely eliminated. This should result in the capacitive reactive power charges being eliminated.
2. Changing the nature of reactive power from capacitive to inductive has increased the consumption of inductive reactive power. However, as the tg(φ) factor < 0.4, there should be no charges for inductive reactive power excesses.
3. The investment in diagnosing the problem and installing the compensator will pay for itself after about 18 months, subsequently saving several thousand zloty per year.

 

Author:
Marcin Szkudniewski