Any deviation of voltage or current from the ideal sinusoidal waveform is a power quality (PQ) disturbance. PQ disturbances can be broadly classified into two categories, Variations and Events. Variations are disturbances which have an effect on every cycle, such as harmonics or voltage unbalance. Events are disturbances which last for a time, from a fraction of a cycle to several cycles, and then may not repeat for several hours or days. Transients and voltage dips are examples of events. It is not economically viable to eliminate PQ disturbances completely. However, they cannot be allowed to become too large, otherwise equipment costs would have to increase to account for the increased immunity required. The basic principles of EMC (electromagnetic compatibility) are used to develop a process by which equipment can be guaranteed to operate satisfactorily on the supply network. The basic idea is that, for each disturbance type, a value called the compatibility level is established and that: • All equipment should have immunity levels greater than the compatibility level. • The PQ disturbance level on the network has to be constrained to be less than the compatibility level. This paper discusses the work undertaken to characterise the emission levels of equipment and electrical network and using this information devise PQ guidelines for the New Zealand electricity industry. The management of emission levels is broadly similar for all disturbance types with some differences in detail. The treatment given in this paper is particularly relevant to harmonics, where a new voltage droop approach is presented. This basically determines a harmonic voltage allocation, which is then converted into a current allocation by assuming a given system harmonic impedance. Different approaches are adopted for LV and MV installations. The main principles are:

1. Time varying harmonic quantities are represented by their 95% values.
2. Diversity between independent sources is represented by the Summation Law.
3. The allocation should increase with customer maximum demand.
4. The allocation should be such that the largest harmonic voltage in the system should reach the planning