Uninterruptible Power Supply UPS Condition Assessment Guidelines

1 Introduction

1.1 General
1.2 Purpose & Intended Users
1.3 Scope

2. References
3. Definitions
4. Safety Measures
5. Instructions
6. Pre-Assessment Activities (Desk Review)
7. Actual Condition Assessment Activities (Condition of UPS Components)
8. UPS Condition Assessment Criteria

Uninterruptible Power Supply UPS Condition Assessment Guidelines

1. Introduction to UPS Condition Assessment

1.1 General

Plant, substation, I.T., or communications UPS systems are crucial devices that supply conditioned power to critical loads, such as communication equipment, DCSs, computers and medical electronic loads. These equipment’s require condition assessment to ensure continuity of power to critical loads, thus avoid the catastrophic failures that could affect the company central business. If UPS systems cannot supply needed conditioned power, plant critical loads will shut down and will not be able to energize protection devices and safety loads, such as communication and medical equipment. This blog give guidelines for assessing the condition of UPS systems. The finding may be used to infer the risk of UPS failure, with related consequences on the central business.

1.2 Purpose and Intended Users

The purpose of this article is to provide guidance to conduct a survey supporting the assessment of the condition of UPS systems. The document will include the list of items to be inspected and how the information can be used to detect potential problems and establish an upgrading plan for existing UPS systems. The main points to be surveyed will be gathered in a checklist form to make the data collection fast and easy. The intended users may include engineers and technicians working in the field of UPS and DC Systems, or people who are involved in repair of power electronics based systems, whether as supporting engineers or power electronics equipment maintenance.

1.3 Scope

This article is written to surveying and assessing Uninterruptible Power Supply (UPS), namely UPS Condition Assessment. It provides guidelines to assign a Failure Risk Score (FRS) utilizing the steps mentioned in this document. The UPS Condition Assessment method is applicable for industrial as well as IT type UPS 10 kVA or larger and their respective static switches.

The UPS Condition Assessment may be requested by operating department once a UPS reached 15 years of age or had undertaken a major operational incident. This blog will help the UPS owner in making lifecycle decisions such as whether to repair, replace, or conduct any other required action to extend the life of aged UPS equipment. This document should be utilized in conjunction with “Guidelines for Minor and Major Preventive Maintenance (PM) of UPS Systems.”

2. References

3. Definitions

UPS system: static uninterruptible power supply, double conversion technology, including backup batteries.
ac: alternate current
dc: direct current
Electrical measurement: Electrical output at specified point
UPS rectifier/charger: Power electronics based device that converts mains ac to dc
UPS inverter: power electronics based device that converts dc from UPS rectifier/charger to ac.

4. Safety Measures of UPS System

UPS equipment contain high voltage, thus only qualified/certified technicians should do any physical activities with the equipment. Hence, make sure that he following safety equipment is provided especially if there are batteries in the room:

 Use adequately insulated tools.
 Be cautious when working on UPS since they represent electric shock hazard.
 Ensure the UPS and battery rooms’ ventilation systems are operational and rooms’ temperature is maintained at 25°C.
 Do not wear metallic object such as jewelry.

5. Instructions

This guide is not intended to define UPS maintenance practices. Guidance and recommendations herein are based on industry standards and practices. However, equipment and situations vary greatly, and sound engineering and management judgment must be exercised when applying these diagnostics. All available information must be considered, for example, manufacturers’ and UPS experts’ recommendations, unusual operating conditions, and personal experience with the equipment in conjunction with this document.

The condition assessment has two steps, pre-assessment activities and actual assessment activities. Both steps determine the Failure Risk Score and help in determining the condition of a certain UPS. The pre-assessment is mainly to do with a non measurement or light assessment where it will focus on desk review, age, local support and visual inspection. Actual assessments will me much more involved in deeper assessment of the UPS.

6. Pre-Assessment Activities

It is the responsibility of the condition assessment leader to make sure that all the following documents are available:
 UPS design and Construction Drawings
 Electrical one line diagram of the UPS and the entire system
 All PM records
 Previous conditions assessment studies

 Start-up procedures
 Commissioning/FAT data if available

The UPS Condition Assessment team leader will make sure that all the information has been reviewed and all documents are available. Pre-assessment will focus on the following:

1. Desk Review
2. Visual Inspection
3. Age
4. Local Support

1 – Desk Review

Desk review is the first essential step in conducting condition assessment where all plant available data as well as commissioning/PM data could tell if the PM was conducted on a timely manner. The method here is not to evaluate the PM, instead the score will be assigned on the availably of the data which means that PM was conducted on a timely manner.

Results of deck review are applied to Table 1 to arrive at an appropriate Condition Score.

Table 1 – Desk Review Scoring

2 – Visual Inspection

Visual inspection is the major milestone to conducting the UPSCA. UPS as well as UPS room, enclosures are among many factors that can be checked visually. The UPS shall be in good condition even if it has been in service for many years. This is also applicable to the UPS static switch. Visual inspection will also include using thermo vision in things does not appear normal or neat.

Results of visual inspection are applied to Table 2 to arrive at an appropriate Condition Score.

Table 2 – Visual Inspection Scoring

3 – Age

The UPS is designed for 20~25 years life time and is expected to serve its design lifetime.

4 – Local Support 

Local support is among the important scores as the unavailability in local support could jeopardize the importance of a UPS. The UPS in intended to provide critical power during emergency and local support should always be available and immediate.

7 Actual Condition Assessment Activities (Condition of UPS Components)

Application of “UPS PM” is required to be able to estimate the condition of the consumable spare parts that affect the integrity of UPS operation. Example of these spares are the dc filter capacitors, the dc smoothing choke, the ac capacitors and choke, the ventilation fans, the automatic circuit breakers, and the tripping units. All these part are consumable and are replaced upon failure or bad condition (exceeding ±10% tolerance). However; it is not industry practice to check the condition of the switching components and smoothing devices such as rectifier SCRs, PCBs, circuit breakers/fuses, inverter IGBTs, and PCBs. These components are always replaceable upon failure and the only concern is the availability of the spare parts for those components.
Also, the time of delivery should be examined during this UPSCA exercise. Table 5 summarizes survey questioner to predict condition of the UPS internal components along with corresponding scoring, as follows.

Table 5 – Survey Questionnaire


8. UPS Condition Assessment Criteria

Sum all scores from both assessment activities of the condition assessment. If result <= 50%, then UPS condition requires attention immediately; whilst replacement consideration is sought. Otherwise, the UPS system should be looked after closely to clear all alarms effectively.


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