Viewing Unbalance Data in the AEMC PEL Control Panel

Introduction

This document explains how to view and interpret unbalance data using AEMC PEL 112, PEL 113, PEL 105, and PEL 115 real-time data in the DataView® PEL Control Panel.

In three-phase AC distribution networks, unbalance (or imbalance) is the ratio of the negative-sequence or zero-sequence component to the positive-sequence (fundamental) component. This ratio, expressed as a percentage between 0% and 100%, can apply to voltage or current. Unbalance percentage indicates distribution network efficiency, and reducing it can lead to significant energy cost savings. For example, the power quality standard EN50160 specifies that unbalance should not exceed 2% at the point of common coupling (PCC).

Positive, Negative, and Zero Sequence

Understanding unbalance data requires familiarity with phase sequence in three-phase networks. These networks have three sets of independent components for current and voltage: positive sequence, negative sequence, and zero sequence.

Positive Sequence

The positive sequence, also called the fundamental component, represents three equal phasors phase-displaced by 120° with the same phase sequence as the original phasors supplied by generators (A-B-C sequence). This component is always present and indicates current flow from source to load.

[Diagram Description: Three vectors labeled A, B, and C originating from a central point. Each vector is separated by 120 degrees, illustrating a balanced three-phase system.]

Negative Sequence

The negative sequence represents three equal phasors, phase-displaced by 120° with each other, but with the opposite phase sequence to the original phasors (A-C-B sequence). This component indicates current flowing from load to source.

[Diagram Description: Three vectors labeled A, B, and C originating from a central point. Vectors A and C are swapped in sequence compared to the positive sequence, with each vector separated by 120 degrees, illustrating an unbalanced system.]

Zero Sequence

The zero sequence represents the component of unbalanced phasors that is equal in magnitude and phase.

[Diagram Description: Three parallel vectors labeled A, B, and C, all pointing in the same direction and having equal length, illustrating the zero sequence component.]

In a balanced three-phase system under normal conditions, only the positive sequence component is present. In reality, three-phase systems are rarely perfectly balanced. Significant unbalance, indicated by a negative sequence, can be harmful to polyphase loads like induction motors.

DataView® PEL Control Panel

To view unbalance data channels for PEL 112, PEL 113, PEL 105, or PEL 115 instruments in the PEL Control Panel, click the "Unbalance" button within the Real-time Data frame. ? NOTE: The "Unbalance" button is only visible for PEL Models 112, 113, 105, and 115.

The Real-time Data frame displays various parameters. The first four are RMS unbalance values:

• Vunb (u0): zero-sequence voltage unbalance
• Vunb (u2): negative-sequence voltage unbalance
• Iunb (i0): zero-sequence current unbalance
• Iunb (i2): negative-sequence current unbalance

Each value is a percentage of its fundamental value. For instance, Vunb (u0) at 37.13% means the zero-sequence voltage is 37.13% of the positive sequence voltage. Similarly, Iunb (i0) at 38.69% means the zero-sequence current is 38.69% of the positive sequence current.

[Diagram Description: A screenshot of the PEL Control Panel software interface. It shows a "Real-time Data" section with columns for RMS values including Vunb (u0), Vunb (u2), Iunb (i0), Iunb (i2), and various Power parameters like P1f, P2f, etc. A bar chart graph is also displayed, showing percentages for P, Pu, PH, Q, and D.]

In an efficient distribution system, unbalance percentages should be close to zero. The example percentages indicate a serious unbalance issue, leading to significant power loss due to network inefficiency.

Below the RMS unbalance data, the Real-time Data frame lists Power parameters. Some parameters may not be displayed depending on the measurement type.

• Pf (P1f, P2f, P3f, PTf): fundamental active power for phase 1, 2, 3, and total.
• PH: harmonics active power.
• P+: total fundamental active power of the positive-sequence power (balanced power).
• Pu: active power of the negative and zero sequence components (unbalanced power).
• Sf (S1f, S2f, S3f, STf): fundamental apparent power for phase 1, 2, 3, and total.
• V+: Positive-sequence phase-to-neutral voltage.
• V0: zero-sequence phase-to-neutral voltage.
• V-: negative-sequence phase-to-neutral voltage.
• I+: positive-sequence current.
• I0: zero-sequence current.
• I-: negative-sequence current.

A histogram (bar chart) below the Power parameters table displays the percentage of P (active power) represented by P+, Pu, PH (harmonic active power), Q (fundamental reactive power), and D (harmonic distortion power).

Power Parameter Relationships

Additional Power parameters can be viewed by clicking the Power button.

• P (P1 , P2, P3, PT): active power for phase 1, 2, 3, and total.
• Q (Q1, Q2, Q3, QT): fundamental reactive power for phase 1, 2, 3, and total.
• D (D1, D2, D3, DT): harmonic distortion power for phase 1, 2, 3, and total.
• S (S1, S2, S3, ST): apparent power for phase 1, 2, 3, and total.

The relationships between these parameters are:

• PTf (total fundamental active power) = P+ (total fundamental balanced power) + Pu (total fundamental unbalanced power)
• PT (total active power) = PTf + PH (harmonics active power)
• S² (apparent power²) = PT² + QT² (total fundamental reactive power²) + DT² (total harmonic distortion power²)

Ideally, P+ should be at or close to 100%. A lower P+ percentage (and thus a higher sum of Pu, PH, Q, and D) indicates greater energy waste in the distribution system. For example, if P+ is 77%, it suggests approximately 23% of the received power is being wasted due to system inefficiencies.

Contacting AEMC® Instruments

For Instrument Repair and Calibration:

Chauvin Arnoux®, Inc. d.b.a. AEMC® Instruments
15 Faraday Drive
Dover, NH 03820 USA
Phone: (800) 945-2362 (Ext. 360) / (603) 749-6434 (Ext. 360)
E-mail: repair@aemc.com
Alternatively, contact your authorized distributor.

For Technical Assistance:

Chauvin Arnoux®, Inc. d.b.a. AEMC® Instruments
Phone: (800) 343-1391 (Ext. 351)
E-mail: techsupport@aemc.com
Website: www.aemc.com