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ES55 Design Standards Q4-04 – Rapid Voltage Changes R.0

Reviewed:

Sergey Kryuchkov Distribution Engineering Scott Merriman Distribution Standards

Valentina Dabic Distribution Planning Warren Quan Distribution Operations, FVO

Raj Solanki Distribution Engineering Garry Walls Distribution Planning

Steven Yau Distribution Standards Cheong Siew Distribution Planning

Josh Patton Distribution Engineering Aaron Ellis Distribution Planning

Travis Brown Distribution Engineering

Q4 – Medium-Voltage Customer Emission Limits ES55 Q Power Quality Page 2 of 10


ES55 Design Standards Q4-04 – Rapid Voltage Changes R.0 Scope

This standard defines the method for determining rapid voltage change (RVC) emission limits for customers connecting to, or requesting connection to, BC Hydro’s public medium-voltage (MV) distribution network. It also describes the assessment process for verifying compliance with prescribed RVC emission limits.

Definitions These terms are used in this section:

Term Definition Steady-State Voltage

State of average r.m.s. voltage which is maintained after all transient effects have subsided.

Ur.m.s.(1/2) Value of the r.m.s. voltage measured over 1 cycle, commencing at a fundamental zero crossing and refreshed each half-cycle.

Ur.m.s.(1) Value of the r.m.s. voltage measured over 1 cycle, commencing at a fundamental zero crossing and refreshed each full-cycle.

Rapid Voltage Change (RVC)

Change in fundamental frequency r.m.s. voltage with duration between 1 and 60 cycles and magnitude less than the sag/swell threshold (10%).

Public Network Low or medium voltage networks are considered ‘public’ when they serve, or are intended to serve, more than one customer from the same transformer.

Private Network Low or medium voltage networks are considered ‘private’ when they serve, and are only intended to serve, one customer from a dedicated transformer.

Electromagnetic Disturbance

Any electrical or magnetic characteristic, either conducted or radiated, that affects the normal operation of equipment, or causes unwanted sensory experiences for people.

Emission Level The level of a given electromagnetic disturbance emitted from a particular device, equipment or system.

Low Voltage (LV)

Describes networks with rated voltage 0 V < Un ≤ 1,000 V.

Medium Voltage (MV)

Describes networks with rated voltage 1,000 V < Un ≤ 35,000 V.



ES55 Design Standards Q4-04 – Rapid Voltage Changes R.0 Application

Q4 is intended for application by distribution planning engineers, regional engineers, designers, and power quality engineers for:

1) Calculation of customer emission limits for approved operation on a BC Hydro-owned public MV network, and

2) Assessment of customer emission performance for confirmation of operational compliance with prescribed limits.

Q4 emission limit determination is valid for all customers connected to, or requesting connection to, a BC Hydro-owned public MV network.

Q4-04 specifically defines BC Hydro’s emission limit requirements for rapid voltage changes.

What are Rapid Voltage Changes? Rapid voltage changes (RVCs) are fluctuations in the fundamental frequency r.m.s. voltages over several cycles. To be characterized as a RVC, the r.m.s. voltage signal must:

originate at some steady state reference value (Uref);

change rapidly to some maximum (±) deviation value (ΔUmax), and

settle at some steady state level, not necessarily the same level it started at (Uend).

Figure 1 illustrates two types of rapid voltage changes.

Figure 1 - Rapid Voltage Changes

RVCs refer only to voltage fluctuations having magnitudes greater than or equal to BC Hydro’s RVC threshold of ±2% and less than the sag/swell threshold of ±10%. Fluctuations greater than or equal to ±10% are characterized as either sags or swells (see Section Q2-08 for BC Hydro’s sag/swell planning limits).




When voltage changes occur in rapid succession, with magnitudes large enough to cause lighting level variations which are noticeable or annoying to human beings, the effect is called flicker (see Section Q3-05). While it is true that RVCs are the root cause of flicker, customer emission limits are required for both RVCs and flicker independently, since it is possible for RVCs to cause disturbance to customers without exceeding flicker emission limits. This is due to the statistical weighting and smoothing which occurs in the IEC flickermeter, and the use of 95% cumulative weekly probability values (CP95) for assessing flicker compliance.

For example, a larger motor start causes a 7% voltage fluctuation on the MV distribution network twice per day. This would cause some lighting level disturbance to customers and would exceed the requirements of this standard which limits RVCs to 6% three or four times per day. However, such performance may not exceed flicker emission limits because use of the CP95 weekly probability value for assessing PST effectively eliminates infrequent outliers from the analysis.

Typical Causes Sudden load changes are the most common causes of RVCs on distribution networks. The cause of sudden load changes may include the following:

protection operation due to electrical fault;

transformer energization;

motor starting;

fluctuating motor torque requirements;

capacitor switching, and

abrupt step load changes.

Effects RVCs, as defined in this standard, would not cause equipment malfunction, damage or failure. The primary effect of, and rationale for, implementing rapid voltage change emission limits is visual discomfort resulting from light flicker.

MV Network Customer Emission Limits Emission limits for RVCs on BC Hydro’s public MV network are applied such that overall network performance complies with planning limits defined in ES55 Q2-04.




All customers connected to, or applying for connection to, BC Hydro’s public MV network are subject to rapid voltage change emission limits.

This section describes the method for allocating emission limits to customers; sample MV-customer emission limit calculations are provided in ES55 Q5-02 for further clarification.

Step 1 – Customer Network Allocation Step 1 consists of determining what portion of network capacity is allocated to the customer installation being assessed. EQ 1 defines how to calculate a customer’s network allocation:

𝑖𝑖% =𝑆𝑆𝑖𝑖𝑆𝑆𝑡𝑡∙ 100 (EQ 1)

Where:

i% = network allocation for customer’s installation. Si = customer’s agreed power (kVA) – See ES55 Q1-04. St = planned MV network apparent power capacity (kVA).

Step 2 – Determination of Customer Emission Limits A customer’s load allocation, as determined in Step 1, is used to determine the customer’s prescribed emission limits for rapid voltage changes as follows:

High-Demand Installations ( i% ≥ 50% ) A customer is considered a high-demand installation when their demand power is equal to, or greater than, 50% of the feeder planning capacity (St).

Customer emission limits are defined in Table 1 for high-demand installations. Table 1 - Rapid voltage change emission limiits for high-demand customers

RVC emission limits (n) Voltage Change ∆U (%)

i% ≥ 50% n ≤ 1 per year [1] 8 < ∆U ≤ 30 [1] n ≤ 8 per year [2] 6 < ∆U ≤ 8 [2]

n ≤ 4 per day 4 < ∆U ≤ 6 n ≤ 2 per hour 3 < ∆U ≤ 4




n ≤ 6 per hour 2 < ∆U ≤ 3

Low-Demand Installations ( i% < 50 ) A customer is considered a low-demand installation when their demand power is less than 50% of the feeder planning capacity (St).

Customer emission limits are defined in Table 2 for low-demand installations. Table 2 - Rapid voltage change emission limiits for low-demand customers

RVC emission limits (n) Voltage Change ∆U (%)

i% < 50% n ≤ 1 per year [1] 8 < ∆U ≤ 30 [1] n ≤ 6 per year [2] 6 < ∆U ≤ 8 [2]

n ≤ 3 per day 4 < ∆U ≤ 6 n ≤ 3 per 2-hours 3 < ∆U ≤ 4 n ≤ 9 per 2-hours 2 < ∆U ≤ 3

Additional Notes Table 1 and Table 2 emission limits are not complete on their own; they must be accompanied by the following notes:

1) Large RVCs/sags are permitted on BC Hydro’s public MV network for transformer energization only, subject to the following rules:

a. RVCs/sags in the range from 8%<∆U≤25% caused by transformer energization are permitted, and

b. Sags in the range from 25%<∆U≤30% caused by transformer energization are permitted only for transformers sized at 1 MVA or smaller. This relaxation is due to uncharacteristically low fault levels in some rural parts of the province.

c. All transformers having energization characteristics which exceed the requirements of categories a) and b) above are required to have inrush current mitigation installed.

2) RVCs in the range from 6-8% caused by customer motor starting may be permitted on BC Hydro’s public MV network with a system operating order in place to restrict equipment operation.

3) Voltage changes ≥ 10% are not classified as RVCs; they are either sags or swells depending on the direction of change. Sags and swells caused by customer equipment operation (other than




transformer energization) are not permitted on BC Hydro’s public LV network.

Performance Criteria

Rapid Voltage Change Measurement The measurement method used for defining frequency and magnitude of RVCs shall be in accordance with the latest version of CAN/CSA 61000-4-30.

The following is required for a valid assessment:

RVC recording should occur during a period when normally fluctuating loads are operational.

The recording period shall be a minimum of one whole week to verify compliance; however, shorter recording periods are valid if they demonstrate non-compliance during normal operation.

Unusual operating conditions – such as network faults – are omitted from the evaluation.

Compliance Assessment There are no statistical criteria used for evaluation of RVC performance; each recorded change is counted and compared against emission limits. Customer performance is assessed for compliance as follows:

Emission limits shall not be exceeded during any interval of the recording period; i.e., a RVC criterion of n ≤ 2 per hour shall not be exceeded during any hour of the assessment (excluding abnormal network operating conditions).

When the assessment interval is > 1 hour or day, the results are not assessed using contiguous intervals. Instead a sliding window approach is used and the interval is assessed at each step:

o The interval length defines the sliding window size (i.e. a 2-hour emission limit corresponds to a 2-hour sliding window);

o The window slides in steps equal to 1 base unit (i.e. a 2-hour sliding window shifts each 1-hour and is re-assessed);

o Additionally, emissions shall not exceed the up-rounded value of n / interval length during any base unit interval. (i.e., for a limit of n ≤ 9 per 2-hours, any 1-hour interval has a limit of 5 rapid voltage changes).




Meter Specifications To determine compliance with RVC emission limits, r.m.s. voltage measurements must be obtained using a power quality meter with Class A performance as defined by CAN/CSA 61000-4-30. Some of the required metering specifications are:

½ cycle r.m.s. voltage measurements are required [Ur.m.s.(1/2)];

Ur.m.s.(1/2) voltage measurements are used to assess over-deviation and under-deviation magnitudes, and

measurement uncertainty shall not exceed 0.1% of the value obtained from the declared supply voltage by a transducer ratio (Udin).

Customer Response When a customer’s operation violates prescribed emission limits on the BC Hydro system, mitigation must occur within 60 days of notification.

Where mitigation requires a complex engineered solution, an extension of time may be granted, at BC Hydro’s discretion, up to 90 days to allow for design, procurement and commissioning of new equipment and/or process.

BC Hydro Power Quality Engineers are available to assist with standards interpretation, data collection and analysis, and compliance evaluation:

They may, where applicable, offer general advice relating to potential mitigation options.

They will not make recommendations of a specific nature for any customer facility.

Customers should act solely on advice from qualified professional electrical engineers, who are hired by the customer, when mitigation is required at their facility.

BC Hydro Response When a customer’s operation violates prescribed emission limits, BC Hydro will notify the customer of their violation. Written notification may be communicated via electronic or regular mail, and the notice will be clear that the customer’s use of electricity is causing a disturbance to the BC Hydro electrical system. Where previous communication has been established electronically between BC Hydro and the customer, email notification shall be considered suitable written notification.




The written notice to the customer should outline that, if a customer fails to meet emission limit requirements within the approved timeframe, then BC Hydro may disconnect the customer from the public network to prevent further disturbing operation. Where upgrades can be installed on the BC Hydro network to mitigate the disturbance, BC Hydro can offer to install such upgrades at the customer’s cost. The customer’s written confirmation for assuming responsibility of these costs should be obtained before installing upgrades for the benefit of the customer.

References − ES55 Q1-04 Customer Apparent Power Assessment

− ES55 Q2-04 Network Planning Limits - Rapid Voltage Changes

Sources − Neilson, J.B., Buchholz, Vern L. BC Hydro Power Quality Guide.

(2005).

− CAN/CSA-C61000-3-7 Electromagnetic compatibility (EMC) - Part 3-7: Limits - Assessment of emission limits for the connection of fluctuating installations to MV, HV and EHV power systems.

− CAN/CSA-C61000-4-30 Electromagnetic compatibility (EMC) - Part 4-30: Testing and measurement techniques - Power quality measurement methods



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