The use of Demand Controllers in the installations served by electric energy supply contracts by the concessionary is a way to guarantee that the system does not exceed the contractual limits, resulting in the application of fines. Small consumers are charged only for the energy used (consumption). Medium and large consumers pay for both the energy and the power made available.

The power appears in the bills of these consumers under the name of demand, which, in fact, corresponds to the average power verified in 15-minute intervals. The National Electrical Energy Agency (ANEEL) is the one that regulates and establishes these parameters in electric energy bills.

But do you know what a Demand Side Controller is and why using this equipment can help your company or industry to be more energy efficient?

What is the Demand Tracker?

The purpose of a Demand Controller is to automatically manage the entrance and exit of loads on the electrical network, in order to prevent consumption exceeding the contracted demand, thus avoiding the payment of fines for excess demand.

The operation of a Power Demand Controller is very easy. The user registers the power value that he has contracted with the concessionaire, and the value of each load that must be managed, that is, turned on and off as needed. From that moment on, the equipment checks from time to time the power consumed in the busbar. Thus, it will turn on and off the loads that are registered so that the power consumed in the busbar is always below the measurement contracted by the concessionary.

The load connection is managed by load line or by schedule, and the demand schedule can be defined on a month-to-month basis. With the

ST8500C

from Alfacomp, for example, you can issue demand control reports via software. In addition, the log memory of this equipment is 60 days and the programming can be done via panel, supervisory, or APP.

Why do demand control in an industry

Doing demand control is indicated because, besides the management of the loads by demand, it allows the management of the loads by schedule. This allows, for example, a genset to be started during peak hours by connecting to a scheduled output per schedule.

A demand controller can also be useful in photovoltaic installations to prevent the injection of excess power into the utility grid. Alfacomp’s supervisory software ensures a history of the installation, giving the manager a tool to analyze its use and consumption of electricity.

The electricity bill for medium and large consumers is made up of the sum of consumption, demand, and overages. The consumption portion is calculated by multiplying the measured consumption by the consumption rate. The demand share, on the other hand, is calculated by multiplying the demand tariff by the contracted demand or by the measured demand (whichever is greater).

The

ST8500C Controllers

controllers have specific features to protect machinery and equipment. Among these is the rest time, which is the time programmed to prevent a load from being turned on again right after it is turned off – which can damage the machine and shorten the life of the contactors (which connect the loads to the electrical grid). The Controllers also allow programming the activation and shutdown of the loads with reverse logic, i.e., shutting down the Controller’s output for active loads, avoiding shutdowns due to control failure.

The demand controller and energy efficiency

The use of demand controls is not restricted to avoiding the fine for breach of contract. It is also interesting as a way of limiting consumption and consequently contingent electricity costs. That is why it is a device to implement energy-efficient industrial operation.

The use of this demand control equipment can bring the benefits of energy management to the consumer, reducing losses and in many cases allowing a reduction in the amount of the energy bill. From the supply point of view, the existence of Demand Side Control in consumer units allows better planning and better use of the distribution system, minimizing investments and increasing the energy efficiency of the sector.

energy efficiency

of the sector.

Pricing

The following are concepts and definitions involved in the pricing system:

• Power: is the consumption capacity of electrical equipment, expressed in Watts (W) or kilowatts (kW).
• Energy: is the amount of electricity used by an electrical appliance when it is left on for a given time. Its most usual units are kilowatt-hours (kWh) or megawatt-hours (Mwh).

The electricity tariff is the composition of calculated values that represent each portion of the investments and technical operations carried out by the agents of the production chain and the necessary structure so that the energy can be used by the consumer. The tariff represents, therefore, the sum of all the components of the industrial process of generation, transport (transmission and distribution), and commercialization of electric energy. In addition, there are charges to fund the application of public policies. The taxes and charges are listed on the electricity bill.

The concession companies supply electric energy to their consumers, based on obligations and rights established in a concession contract, entered into with the Federal Government, for the exploration of the public service of electric energy distribution in its concession area. At the time of signing the contract, the concessionaire recognizes that the current tariff level, i.e. the tariffs defined in the company’s tariff structure, together with the tariff adjustment and revision mechanisms established in that contract, are sufficient for the maintenance of its economic-financial balance (ANEEL, 2019).

Pricing methods refer to the way that consumers are classified in order to be charged for their electricity consumption. For the same, one should observe the tariff structure and consumer groups (PROCEL, 2011).

Tariff Structure

The tariff structure is a set of tariffs (price list) applicable to the electric power consumption and/or power demand components, according to the supply modality. It seeks to reflect the differences in costs related to the supply of energy to each type of consumer. From then on, the relativity of prices is defined. The structure comprises the differentiation of tariffs, according to consumption and demand components, supply voltage level, consumption class, season, period of the day, consumer location, etc. (BITU; BORN, 1993).

Electricity tariffs do not have the same value for all consumers. They are differentiated among tariff groups, according to the supply voltage, the moment of consumption, the type of tariff, and the consumer class. They can be structured and differentiated in many ways (VIEIRA, 2016).

Theoretically, a tariff could be defined for each consumer, but difficulties of various natures, such as, for example, the restrictions of commercialization, measurement system and collection, limit the degree of improvement of the tariff structure.

The consumer pays a final price that includes, in addition to the rates, fees or charges, contributions and taxes that are taxes, i.e., mandatory payments that do not represent a punishment for wrongdoing and must be provided by law (FUGIMOTO, 2010).

The fees or charges are independent of the amount of energy consumed and are related to the costs of servicing the consumption units. They are related to the costs associated with serving consumers, directly at the consumption units.

There are special rates such as those related to the additional fuel consumption in thermal power plants. The fees allow unforeseen increases in costs to be passed on to the consumer quickly. The final supply price paid by the customer is the composition of the tariff, contributions, fees, with taxes such as ICMS (FUGIMOTO, 2010).

Consumer Classification

For billing purposes, the consumer units are grouped into two tariff groups, defined mainly in function of the supply voltage and also, as a consequence, in function of the demand. If the utility supplies power at a voltage below 2300 Volts, the consumer is classified as being from “Group B” (low voltage); if the supply voltage is greater than or equal to 2300 Volts, the consumer is from “Group A” (high voltage). These groups were defined thus:

Group A Consumers

Group consisting of consumer units supplied at a voltage equal to or above 2.3 kV, or, also, supplied at a voltage below 2.3 kV from an underground distribution system and billed in this Group, on an optional basis, as defined in ANEEL Resolution 456, characterized by the binomial tariff structure and subdivided into subgroups A1, A2, A3, A3a, A4 and AS. The table below presents these subgroups.

Subgroups	Tension
A1	Supply voltage equal or higher than 230 kV
A2	Supply voltage from 88 kV to 138 kV
A3	Supply voltage 69 kV
A3a	Supply voltage from 30 kV to 44 kV
A4	Supply voltage from 2.3 kV to 25 kV
AS	Supply voltage below 2.3 kV served from an underground distribution system and included in this Group on an optional basis.

Consumers in this group are charged for both the demand and the energy they consume. These consumers can fall into one of two tariff alternatives:
– Conventional pricing;
– Hourly-seasonal pricing.

Conventional Pricing

The framing of the conventional tariff requires a specific contract with the concessionaire in which a single value of demand intended by the consumer (contracted demand) is agreed upon, regardless of the time of day (peak or off-peak) or the period of the year (dry or wet).

Consumers in Group A, subgroups A3a, A4 or AS, may be included in the conventional tariff when the contracted demand is less than 300 kW, as long as there have not been, in the previous 11 months, 3 (three) consecutive records or 6 (six) alternate records of demand over 300 kW.

The electric energy bill for these consumers is composed of the sum of consumption, demand, and overages. The consumption portion is calculated by multiplying the measured consumption by the consumption rate.

The demand share is calculated by multiplying the demand tariff by the contracted demand or by the measured demand (the higher of the two), if it does not exceed the contracted demand by 10%.

The overage portion is charged only when the measured demand exceeds the contracted demand by more than 10%. It is calculated by multiplying the overage tariff by the value of the measured demand that exceeds the contracted demand (BRASIL, 2000).

Horo-Seasonal Pricing

This modality is characterized by the application of differentiated tariffs for electric power consumption and power demand according to the hours of use of the day and the periods of the year.

The hour-seasonal charging structure can be applied according to the following charging models:

a) Green Rate

The Green tariff for Group A consumers. This tariff mode requires a specific contract with the concessionaire in which the demand desired by the consumer (contracted demand) is agreed, regardless of the time of day (peak or off-peak). Although not explicit, Aneel’s Resolution 414 of 2010 allows two different demand values to be contracted, one for the dry period and another for the wet period (BRASIL, 2010). The electric energy bill for these consumers is composed of the sum of consumption (on- and off-peak), demand, and overages.

The demand share is calculated by multiplying the demand tariff by the contracted demand or by the measured demand (the higher of the two) if it does not exceed the contracted demand by more than 10%. The demand charge is unique, regardless of the time of day or period of the year.
The overage portion is charged only when the measured demand exceeds the contracted demand by more than 10%. It is calculated by multiplying the overage tariff by the value of the measured demand that exceeds the contracted demand.

b) Horo-seasonal Blue Fare

The inclusion of Group A consumers in the hourly blue tariff is mandatory for consumers of subgroups A1, A2 or A3. This tariff modality requires a specific contract with the concessionaire in which both the value of the demand intended by the consumer during peak hours (peak contracted demand) and the value intended during off-peak hours (off-peak contracted demand) are agreed upon.

Although not explicit, as with the green tariff, Resolution 414 allows different values to be contracted for the dry period and the wet period (BRASIL, 2010).

The electric energy bill for these consumers is composed of the sum of the parts referring to consumption and demand and, if any, overages. In all plots the differentiation between peak and off-peak hours is observed (CENTRAIS ELÉTRICAS BRASILEIRAS, 2011).

The demand portion is calculated by adding the product of the on-peak demand charge and the on-peak contracted demand (or the on-peak metered demand, subject to overshoot tolerances) to the product of the off-peak demand charge and the off-peak contracted demand (or the off-peak metered demand, subject to overshoot tolerances).

The demand charges are not differentiated by period of the year. The overage portion is charged only when the measured demand exceeds the contracted demand above the tolerance limits of 5% for the A1, A2 and A3 sub-groups and 10% for the other sub-groups. The value of this portion is obtained by multiplying the overage charge by the value of the metered demand that exceeds the contracted demand (PROCEL, 2011).

Group B Consumers

Consumer units served at voltage below 2.3 kV, or even units served at voltage above 2.3 kV and billed in this group, are characterized by the monomial tariff structure (ANEEL, 2000).

A group B consumer is one who receives electricity at a voltage between 220 and 380 V and has an adhesion contract with the energy concessionaire. Adhesion contract is a contractual instrument, with clauses bound to the norms and regulations approved by ANEEL, the content of which cannot be modified by the concessionaire or consumer, to be accepted or rejected in full (ANEEL, 2000).

Group B consumers (low voltage< 2,300 Volts) are classified as:

• B1 – residential;
• B2 – rural;
• B3 – other classes;
• B4 – public lighting.

Low voltage consumers (Group B) are further classified according to the number of phases. There are three types of supply, depending on the number of phases:

• Type A – single-phase – two conductors (one phase and neutral);
• Type B – two-phase – three conductors (two phases and neutral);
• Type C – three-phase – four conductors (three phases and neutral).

To determine these, the installed load of each consumer unit must be calculated. This load will be the sum of the rated plate powers of the electrical appliances and the declared lighting powers. When there are motor loads, their respective quantities and individual powers should be computed (PROCEL,2011).

In Group B consumers, only energy consumption is billed, and there is no charge for power demand (PROCEL, 2011).

Off-peak and Peak Times

Peak time (P) is the period defined by the distributor and composed of three consecutive daily hours, except for Saturdays, Sundays, Carnival Tuesday, Passion Friday, Corpus Christi, and eight holiday days as described in ANEEL Resolution 414, considering the load curve of its electrical system, approved by ANEEL for the entire concession area. The off-peak hour (F) is the period composed of the set of consecutive and complementary daily hours to those defined in the peak hour (VIANA; BORTONI; NOGUEIRA, 2012).

Peak and Off-Peak times for a consumer unit

Source: Viana, Bortoni, and Nogueira (2012).

Also according to Viana, Bortoni, and Nogueira (2012), these schedules are defined by the concessionaire due mainly to its supply capacity. The typical power supply curve of a utility can be seen through the figure below, where the highest demand value usually occurs during peak hours.

Typical power supply curve of a utility

Source: Viana, Bortoni, and Nogueira (2012).

Dry and Wet Periods

These periods are normally directly related to the periods where the flood variations of the water reservoirs used for power generation occur. The Dry Period corresponds to the period of 07 (seven) consecutive billing cycles, starting in May and ending in November of each year; it is, generally, the period with little rain. The Wet period corresponds to the period of 05 (five) consecutive billing cycles, comprising the supplies covered by the readings from December of one year to April of the following year; it is generally the period with more rainfall (CARVALHO, 2011).

Electricity demand

According to ANEEL’s Resolution 456 in Art. 2º, § VIII, demand is the average of the active or reactive electric powers requested to the electric system by the installed load portion in operation at the consumer unit, during a specified time interval. Thus, this average power, expressed in kilowatts (kW) and kilovolt-ampere-reactive (kvar), respectively. It can be calculated, for example, by dividing the electrical energy absorbed by the load in a certain time interval Δt, by this time interval Δt, and can be expressed by the equation below.

In Brazil the time interval (integration period) is 15 minutes, so in one month we will have: 30 days x 24 hours / 15 minutes = 2880 intervals (ANEEL, 2019).

According to Suppa and Terada (2010), we have synchronous and asynchronous measurement methods. The synchronous measurement method is the one used by all Brazilian utilities and by most countries, measuring active power in a certain time interval that can vary from 15 to 60 minutes in most cases.

In practice, what is done is to integrate the energy pulses within this interval, therefore called integration interval, obtaining what we call active energy demand, that is, the demand is the average energy consumed in each 15-minute interval not fully existing before the interval closes.

Generally, the utility bills for the highest values registered in the off-peak and peak periods or for the contracted values, whichever are higher. At each start of the integration interval the consumption is reset to zero, starting a new countdown. If at the end of the interval the average closing value exceeds the allowed limit, the user will face heavy fines for exceeding the limit.

Also according to the resolution, some definitions are adopted between the distributor and the consumer through a service provision contract, and they are (ANEEL, 2019):

• Demand: average of the active or reactive electric power demanded from the electric system by the installed load portion in operation at the consumer unit, during a specified time interval.
• Contracted demand: active power demand to be compulsorily and continuously made available by the concessionaire, at the point of delivery, according to the value and period of validity established in the supply contract and which must be fully paid for, whether it is used or not during the billing period, expressed in kilowatts (kW);
• Exceeding demand: portion of the measured demand that exceeds the value of the contracted demand, expressed in kilowatts (kW);
• Measured demand: highest active power demand verified by measurement, integralized in an interval of 15 (fifteen) minutes expressed in kilowatts (kW);
• Billable demand: active power demand value identified according to the criteria established and considered for billing purposes, with the application of the respective tariff, expressed in kilowatts (kW).

For consumption billing, the total kWh consumed during the period is accumulated: off dry peak or off wet peak, and dry peak or wet peak. For each of these periods, a differentiated consumption tariff applies, and the total is the consumption billing portion. Evidently, consumption tariffs in dry periods are higher than in wet periods, and during peak hours is more expensive than during off-peak hours (PROCEL, 2011).

The charge is always a function of contracted demand and consumption. When you contract a demand, you are actually requesting that the supplying company makes a certain amount of energy available to be consumed. In this way, three cases of charging may occur (PROCEL, 2011):

• Registered demand lower than the contracted demand: the consumption and demand tariff corresponding to the contracted value applies;
• Registered demand higher than the contracted demand, but within the overrun tolerance: the consumption and demand tariff corresponding to the demand applies
• Registered demand higher than the contracted demand and above the tolerance: the consumption and demand tariff corresponding to the contracted demand is applied, and to this is added the application of the overage tariff, corresponding to the difference between the registered demand and the contracted demand. In other words, you pay the normal charge for the contracted service, and an overage charge on all the excess.

Demand Exceedance

According to Aneel (2018), energy demand is contracted with the utility (you pay for it regardless of usage). The demand monitoring is done by the average of the 15 minutes of integration. Its measurement is based on the “average” of the 15 minutes of demand integration. The exceeding of the electric demand is controlled based on the average values of the 15 minutes integration, that is, the average demand of 15 minutes cannot exceed the contracted demand. If the overrun occurs, the concessionary will charge the fine based on the highest recorded value. According to the type of consumer, there is a tolerance on the contracted demand value so that no fines are charged, as defined in Resolution 456 of November 29, 2000, Art. 2, § VIII:

• 5%, for units with a supply voltage greater than or equal to 69 kV (blue tariff);
• 10%, for units whose supply voltage is lower than 69 kV and in the billing month, the off-peak demand (blue tariff) and the demand (green tariff), are higher than 100 kW;
• 20%, for units served at a voltage of less than 69 kV, and in the billing month, off-peak demand (blue tariff) and demand (green tariff) from 50 to 100 kW.

Demand Control

According to F.S Ozur (2011), The demand controller is an electronic equipment whose main function is to maintain the active power demand of a consumer unit, within predetermined limit values, acting, if necessary, on some part of the Demand Controllers also controls the power factor and energy consumption. Controlling the demand is fundamental, not only for the consumer to reduce his costs with electric energy, but also for the concessionaire that needs to operate in a well-dimensioned way, avoiding interruptions or poor supply quality.

Example of a demand controller

The ST8500C demand controllers were developed by Alfacomp to, through continuous monitoring and proper load management, keep the electrical power within pre-set limits.

Programming and operating the equipment is very simple, because it is compatible with other important tools, such as standard energy meter interfaces, according to the ABNT NBR14522 standard.

In addition, the ST8500C measures and records various electrical quantities (memory for 30 days of records), providing the user with a complete examination of your facility’s power system. It is also possible to use the equipment in conjunction with the ST-Conecta software (software that comes with the product), which allows maximizing the data analysis and management.

More than just power demand controllers, the ST8500C devices are powerful electric power management systems.

Principle of operation

The ST8500C controllers receive continuous load power information through the serial user interface, opto-coupled, standardized through the NBR14.522 (ABNT) standard, available in power electronic meters. The information, in the model with CT’s, can be passed on via the electrical bus connection, with the use of current transformers (CT X/5) and voltage signals. The electrical energy demand of the load is calculated using mathematical algorithms.

As needed, that is, whenever the projected demand is above the set-point, the ST8500C controllers deactivate one or more loads, promoting their correction. In the same way, every time the projected demand falls below the stipulated level, the controller activates one or more loads.

The ST8500C controllers have several features aimed at protecting your machines and equipment. Among these is the rest time, which is the time programmed to prevent a load from being turned on again right after it is turned off – which can damage the machine and shorten the life of the contactors (which connect the loads to the electrical grid). The controllers also allow you to program the activation and shutdown of the loads with reverse logic, i.e., shutting down the controller output for active loads, avoiding downtime due to control failure.

Visual inspection

Before installation, make a careful visual inspection to make sure that the product has not been damaged in transit.

Electrical Wiring Diagrams

The following figures show the connection schemes of the ST8500C controllers.

1. model with CT input

2. Model with opto-coupled input

Drive Connections

Important notes on equipment installation

• In the model with current transformers (CTs), the transformation ratio should be X/5A.
• Each contactor drive must be protected with an individual fuse.
• The wiring that measures voltage should be placed in separate conduits from the contactor control with a distance of at least 10 cm.
  The wiring should also not pass through the power cable ducts, where the load current will circulate.
• Be careful about the supply voltage and the way the contactors are connected. The common wire of the contactors must be different from the one used
  on the controller’s power supply. Remember that the maximum voltage/current for each drive output is 250VAC/5A.
• The maximum supply voltage of the controller, which is used for the equipment to work, is 270VAC, while the measurement voltage,
  used for calculations for display information, can go up to 600VAC.
• In the opto-coupled model it is necessary to apply voltage to the measurement input in order to display them in the electrical measurements menu,
  both the voltage parameter and the current parameter. Otherwise, these two parameters will be reset to zero.

Attention!

The ST8500C’s voltage supply can be from any source, as long as it stays within the range of 80 to 270 VAC.

Demand controller front panel

NOTE: The ST8500C display backlighting is only activated when a key is pressed. If no key is pressed within 3 minutes, the lighting will turn off automatically.

LED indicators

• OK Equipment on
• ST Lit, indicates an active alarm
• RX Indicates serial channel receiving data
• TX Indicates serial channel transmitting data

REFERENCE

• What is a Demand Side Controller and why use it in industry – https://sultech.com.br/2021/04/29/o-que-e-um-controlador-de-demanda-e-porque-utilizar-na-industria/

• ENERGY DEMAND CONTROL OF AN INDUSTRIAL ELECTRIC SYSTEM – EZEQUIEL COSER – Lajeado, November 2019

• Agência Nacional de Energia Elétrica – ANEEL, “ANEEL NORMATIVE RESOLUTION No. 1,000, OF DECEMBER 7, 2021”. [Online]. Available: https://www.in.gov.br/en/web/dou/-/resolucao-normativa-aneel-n-1.000-de-7-de-dezembro-de-2021-368359651. [Acesso em 11 abr 2022].

Read more