Application to "Guideline for Suppressing Harmonics by the Users Who Receive High Voltage or Special High Voltage"

In principle, the guideline applies to the customers that meet the following two conditions:

• The customer receives high voltage or special high voltage.
• The "equivalent capacity" of the converter load exceeds the standard value for the receiving voltage (50kVA at a receiving voltage of 6.6kV).

The level (calculated value) of the harmonic current that flows from the customer's receiving point out to the system is subjected to the regulation. The regulation value is proportional to the contract demand. The regulation values specified in the guideline are shown in Table 1.

Table 1 Upper limits of harmonic outflow current per kW of contract demand [mA/kW]

1. Calculation of Equivalent Capacity (Pi)

Although the equivalent capacity (Pi) is calculated using the equation of (input rated capacity) x (conversion factor), catalog of conventional inverters do not contain input rated capacities. A description of the input rated capacity is shown below:

• Calculate the input fundamental current l1 from the kW rating and efficiency of the load motor, as well as the efficiency of the inverter. Then, calculate the input rated capacity as shown below:
  Input rated capacity = 3 x (power supply voltage) x I1 x 1.0228/1000[kVA] Where 1.0228 is the 6-pulse converter's value obtained by (effective current) / (fundamental current).
• When a general-purpose motor or inverter motor is used, the appropriate value shown in Table 2 can be used. Select a value based on the kW rating of the motor used, irrespective of the inverter type.

Table 2 "Input rated capacities" of general-purpose inverters determined by the nominal applied motors

• Depending on whether an optional ACR (AC REACTOR) or DCR (DC REACTOR) is used, apply the appropriate conversion factor specified in the appendix to the guideline. The values of the converter factor are shown in Table 3.

Table 3 "Conversion factors Ki" for general-purpose inverters determined by reactors

2. Calculation of Harmonic Current

• Apply the appropriate value shown in Table 4 based on the kW rating of the motor, irrespective of the inverter type or whether a reactor is used.
  * If the input voltage is different, calculate the input fundamental current in inverse proportion to the voltage.

Table 4 "Input fundamental currents" of general-purpose inverters determined by the nominal applied motors

Table 5 Generated harmonic current [%], 3-phase bridge (capacitor smoothing)

• ACR: 3%
• DCR: Accumulated energy equal to 0.08 to 0.15ms (100% load conversion)
• Smoothing capacitor: Accumulated energy equal to 15 to 30ms (100% load conversion)
• Load: 100%

n nth harmonic current [A] = Fundamental current [A] x
Calculate the harmonic current of each degree using the following equation:

• For a load for elevators, which provides intermittent operation, or a load with a sufficient designed motor rating, reduce the current by multiplying the equation by the "maximum availability factor" of the load.
• The "maximum availability factor of an appliance" means the ratio of the capacity of the harmonic generator in operation at which the availability reaches the maximum, to its total capacity, and the capacity of the generator in operation is an average for 30 minutes.
• In general, the maximum availability factor is calculated according to this definition, but the standard values shown in Table 6 are recommended for inverters for building equipment.

Table 6 Availability factors of inverters, etc. for building equipment (standard values)

[Correction coefficient according to contract demand level]
ï Since the total availability factor decreases with increase in the building scale, calculating reduced harmonics with the correction coefficient s defined in Table 7 below is permitted.

Table 7 Correction coefficient according to the building scale

*If the contract demand is between two specified values shown in Table 7, calculate the value by interpolation.

Calculate only the "5th and 7th" harmonic currents