Combined Heat & Power Plant Connection into Distribution Network According to Least Cost Technically Acceptable Principle

Abstract

The aim of this paper is to give insight in the Combined Heat and Power (CHP) plant connection method into the Distribution Network (DN) based on Least Cost Technically Acceptable (LCTA) principle and impact of the most dominant DN technical, operational and economic constraints that influence the connection method.Due to increasing population growth and concerns for environmental pollution and climate change, the current DNs is facing the challenges of increasing demand, environmental protection, high reliability requirement, cleanness of energy, and planning restrictions. As a potential solution for these concerns, centralized generating facilities are transformed into smaller and more distributed unit. However, indiscriminate usage of such units can also be detrimental for the DN operation.The design/operation of a CHP system is inherently complex since it involves a balancing act between the amount of power and usable heat that CHP system delivers vs the amount of heat and power needed by the end use for that energy. While the power to heat ratio (P/H) of the CHP system may be reasonably constant, that is often not the case for the end-user for whom the demand for heat and for power often varies with the seasons and also it may vary throught the day.Connection costs can make up a significant proportion of CHP system project costs and may therefore have major impact on the financial viability of a CHP generation scheme and the local DN into which the CHP system would be looking to connect. Specifically, factors such as the location of the scheme, connection voltage, the rated capacity of the existing DN, the existing demand for electricity in the area and export capacity of the of the prosumers will be likely to have an impact on the connection cost.There is no general agreement regarding the practice concerning the optimal allocation of financial responsibility for the CHP plant connection cost in the DN. The differences in policies for the connection charges are substantial. They reflect the fact that different connection principles and policies consideration, each reasonable and valid, lead to different conclusion. The main goal of the planning process is to ensure that the DN is developed in an orderly and cost effective way; Distribution Network planner (DNP) and Distribution Network Operator (DNO) must ensure that there is sufficient DN capacity available to meet new loads and CHP system connection as they arise, and to meet on-going growth and requirements. They also need to ensure that new connections are completed as technically/economically acceptable and able to meet the possible future needs of the customer/prosumers. DNO is obliged to provide the CHP system developer with connection under acceptable standards as detailed in the DN Distributed Code. If higher standard or higher security of CHP generation connection is required it can be provided at the CHP system developer’s request, however the full additional costs will be assign to the developer. In order to complete the CHP system connection into the DN according to the LCTA principle the following sensitivity analysis of technical constraints are necessary to be performed as part of the connection process and these include: Equipment ratings, Protection settings, Voltage profile and Network losses. Based on the results obtained from these sensitivity analysis the DNP/DNO will determine a connection method which complies with the DN appropriate standards and planning criteria.