and could lead to breaker damage if not replaced on time. • Self-monitoring is done on current measurements and tripping circuits. In case of failure, investigation and repair is done in a timely manner to minimise the risk of larger failures. UPS (Uninterruptible Power Supply) UPS systems needs regular monitoring and maintenance to ensure maximum reliability. The battery is the most vulnerable part of any single UPS system, regardless of its capacity, topology or brand. Understanding the causes of battery degradation is important to prevent failure, and maintenance actions are fundamental to ensuring the highest system availability. Reasons for batteries prematurely failing in a single UPS system can be: • The number of charging and discharging cycles affects the service life of the battery. • Improper charging and discharging – the lifetime of a battery can be greatly affected by the current and voltage control on the battery during charge and discharge cycles. • Batteries will have a shorter life when operated at a higher temperature. Drives Variable speed drives are used to enable smooth process control and energy savings. Hundreds of pumps and fans are controlled with drives; their reliability and availability have a major impact on plant productivity. Failures typically cause production slowdown or full stoppage. Drives are electronic devices where REMOTE MONITORING SYSTEMS WORLD PULP&PAPER 34 Knowing how equipment has been used and in which environmental conditions are key to making smart maintenance decisions that will improve OEE be detected and the appropriate maintenance planned. • Self-monitoring of protection relays indicates internal or protection circuit failure which should be investigated and repaired quickly to minimise the risk of larger failures. • Protection system coordination in failure situations can be validated against design values when detailed recorder data is stored and easily available. Low voltage breakers Low voltage breakers have built-in protection with additional condition monitoring features. When breakers are operated several times per hour, it leads to a need for more frequent maintenance between scheduled plant shutdowns. Based on breaker operation and condition, data-driven decisions can be made to improve reliability, for example: • Maintenance interval of installed 800A to 5000A breakers is between 1500 to 5000 operations. The number of operations is used to schedule the next time for maintenance. In some applications, breakers may be heavily operated; this could lead to a situation where maintenance is needed much earlier than scheduled in the maintenance management system. Active monitoring provides warnings in these situations in order to schedule maintenance at the right time. • Breaker internal contact wear monitoring is used for estimating the maintenance need. Numerous full load operations of breakers cause excessive wear on contacts staff is the most important requirement for a condition monitoring system. The electrical system in this user case is monitored in such a way to support the mill’s overall OEE objectives. The following sections describe the monitoring methods by equipment category. High and medium voltage Modern protection relays monitor the electrical network and protect it in a failure situation to limit impact to the smallest possible area. Today, relays are also used as a data source to monitor switchgear and breaker operation and condition. Breaker maintenance is usually based on the number of operations and other measurable values. Typically these operations are being measured by protection relays, but not efficiently collected and utilized for maintenance decisions. Examples of monitoring points for high and medium voltage equipment in this case: • ANSI and IEC standards define circuit-breaker mechanical endurance ratings that impact mechanism designs, and typically range from 1,500 to 10,000 operations. Information on the number of operations is directly used to schedule next breaker maintenance. • Inactive time indicates in days how long a breaker has not been operated and could result in the need to open and close it to validate its functionality. • Breaker wear is determined by how many normal and short- circuit operations the breaker has experienced. Excess wear can