Intelligent LV switchboards

Distribution of electrical power

In all buildings, regardless of the activity carried out inside, the distribution of electrical power must today satisfy ever-increasing needs for dependability and efficiency. Energy must be available not only to ensure the comfort and safety of users, but also to avoid the costs incurred by power failures.

Electrical installations must therefore be monitored and be capable of reacting automatically to optimise power distribution. Information processing makes this possible.

Already used in medium-voltage industrial and public-distribution applications, digital control and monitoring is now becoming a reality for low-voltage installations as well. Starting with an analysis of needs, this «Cahier Technique» takes a close look at how LV power distribution can be managed. Particular emphasis is placed on decentralising and distributing intelligence in and around the LV switchboard. Several examples of such installations are also provided.

Introduction

For whatever type of application, whether in office buildings, banks, hospitals, supermarkets, airports, tunnels or industrial sites, the need to monitor and control electrical installations is increasingly prevalent, to ensure the following:

• safety,
• availability of power,
• optimisation of energy consumption and costs (depending on the energy supplier’s tariff schedules),
• reduction in operating and maintenance costs;
• ease of operation,
• maintainability and upgradeability of the electrical installation.

Power management can today be implemented by a Digital Control System (DCS) designed to meet all the above needs. Power management may be combined with the management of other facilities:

• building management (access control, airconditioning and heating, anti-intrusion systems, lighting …),
• digital control and monitoring of industrial processes.

Due to the wide range of needs and significant technological progress over the last few years, a number of solutions are today available when designing systems to monitor and control electrical installations. It is now possible to arrive at a judicious balance between needs and the corresponding solutions through the use of digital communications buses and the integration of microprocessors in electrical equipment. «Cahier Technique» n° 156 explains how to design the power section of an electrical switchboard so that it satisfies needs concerning dependability.

The goal of this document is to discuss the optimised design of power-management systems in LV electrical installations. The first step is to review the needs expressed by users and operators.

Needs

The needs of users and operators of electrical installations are different, depending on whether the building is intended for commercial, industrial or infrastructural purposes. A hierarchy of needs may be established (see fig. 1 ). For example, in a small office building, the cost of energy and ease of use of systems by nonspecialists are the foremost criteria.

Energy costs

A constant concern for all companies is the need to reduce the cost of energy. Reductions may be achieved by working on two different factors, the level of consumption and the pricing system of the energy supplier. To that end, in-depth knowledge is required on daily and seasonal fluctuations, as well as on power and consumption levels. A measuring system providing digital data for use on a supervision screen is required to monitor and analyse the above elements.

It is then possible to:

• undertake action to improve the situation,
• check the effects of the action taken,
• determine energy costs per workshop, department, etc.
• Reduce consumption

There are numerous possibilities, depending on the type of application:

• turn off lighting and reduce heating in unoccupied rooms,
• use motors equipped with variable-speed drives for industrial applications,
• use conditioners and/or filters to reduce losses due to harmonic and capacitive currents in cables and transformers.
• Reduce costs related to the terms of the contract with the energy supplier
• use capacitor banks to avoid being billed for reactive power

Managing consumption and energy costs is another function of power-management systems.

AUTHOR: Schneider Electric expert | Antoine JAMMES