NEMA - MG 10011
Power Index Calculation Procedure— Standard Rating Methodology for Power Drive Systems and Complete Drive Modules
| Organization: | NEMA |
| Publication Date: | 1 January 2022 |
| Status: | active |
| Page Count: | 26 |
scope:
This standard establishes the calculation procedure and metric of Power Index (PI) for low voltage (600 V and less) power drive systems (PDS) and complete drive modules (CDM) from 1 to 500 HP.
The rated PDS consists of the combination of a CDM and a motor. The CDM is an electronic power converter connected between the single or polyphase AC supply and a polyphase motor. The motor is any motor that can be tested according to IEC 60034-2-3. It includes any controls as packaged by the manufacturer at the time of sale. The PDS as rated does not include connected driven equipment. It includes all components from incoming power to torque output from the motor shaft. See Figure 1.
The PI calculated using this document can be applied to any of the following cases:
a. Case 1: A PDS consisting of an integrated motor and control (IMAC) where the controls are housed on the motor casing
b. Case 2: A paired PDS consisting of a CDM packaged and sold with a physically separate motor
c. Case 3: A CDM-only (PI rating is calculated using a Default Motor).
Cases 1 and 2 are rated in the same manner. The only difference for Case 3 is that for a CDM-only, PI uses the losses from the Default Motor as given in Table 4.
The PDS, as rated, does not include any gears, belts, or other transmission of torque. This specifically excludes any magnetic, hydraulic, or other non-electronic drive. Servo motors are specifically excluded. For the purposes of this rating, the scope is limited to low voltage (under 600V) equipment and motors with a "Premium Efficiency" rating or above.
There are several fundamental concepts that describe the potential power reduction and energy savings that can be expected from a given PDS in a given application:
a. The power-speed relationship or torque type of the driven equipment (can be variable or constant)
b. The variability of the operating point in the application or load profiles (can be variable or constant) and
c. The variability of the operating speed of the motor/drive (can be variable or constant.)
The following tables describe the differences in torque types, load types, and speed types as used in this document. Each of these terms is also defined in Section 3.
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