Futuros desarrollos

• Fundamental Properties of Electric Circuit . . . 3-2

• AC Circuit Basics . . . 3-2

• Circuit Impedance . . . 3-3

• Power Factor . . . 3-3

• AC Power . . . 3-5

• Phase Converters . . . 3-5

• High Voltage Surge Arrestor . . . .3-6 3B INDUCTION MOTORS

• Induction Motor Overview . . . 3-7

• Voltage . . . 3-9

• Frequency . . . 3-11

• AC Power . . . 3-12

• Motor Output Rating . . . 3-12

• Efficiency . . . 3-15

• Three Phase Motors . . . 3-17

• Three Phase Unbalance . . . 3-19

• Single Phase Motors . . . 3-21

• Power Factor . . . 3-21

• Power Factor Correction . . . 3-22

• Environmental Considerations . . . 3-23

• Insulation Systems . . . 3-25

• Rules of Thumb . . . 3-26 3C MOTOR STARTING

• Full Voltage Starting . . . 3-27

• Reduced Voltage Starting . . . 3-27 3D GRUNDFOS CONTROLLERS

• CU3 Motor Controller & Protector . . . 3-33

• CU3 Technical Specifications . . . 3-35

• CU3 with R100 Remote Control . . . 3-35

• R100 Menus . . . 3-35

• R100 Menu Structure Screen . . . 3-36

• CU3 with SM100 Sensor Module . . . 3-38

• G100 Gateway Communications Interface . . . 3-38

• G100 Network . . . 3-40

• G100 Technical Data . . . 3-41

Section 3

3A ELECTRICAL FUNDAMENTALS

This section is not an attempt to present a course in electricity, and is intended as a review of the terms and basic formulas associated with submersible pumping applications. In the application of electrical driven submersible pumps, we are principally concerned with alternating current (AC) as it relates to three phase (3ph) power and to a lesser degree on single phase (1p) AC circuits. Direct current (DC) circuits are directly analogous to 1 ph AC circuits when reactance is accounted for.

Fundamental Properties of Electric Circuits

Electricity is basically electrons in motion. Electromotive forces cause free or loosely bound electrons to move along or through a medium. Materials such as aluminum, copper, silver and gold allow electrons to move freely and are called conductors. Materials such as porcelain, glass, rubber, plastics, and oils resist electron movement and are called insulators.

Forces that move electrons are magnetic. Moving a conductive wire in a way that cuts across a magnetic field induces a force or voltage in the wire. If there is a path for the electrons to follow, a flow will be established. The

strength of the electro-motive forces (emf) is defined in volts and is analogues to pressure in a hydraulic system. The magnitude of electron flow is called current and is measured in amperes, which is analogus to fluid flow. The resistance to current flow is

analogous to the friction loss of water flowing through a pipe and is measured in ohms. Voltage, current, resistant and power are related to each other by Ohm’s law. Ohm’s law in its most basic mathematical form is expressed as: E = IR and P = EI; where E = voltage (V), I = current (A - amps), R = resistance (ohms) and P = power (W - watts). Figure 3-1 illustrates the various electrical values derived from ohms law.

AC Circuit Basics

AC circuits differ form DC circuits in that voltage and current follow an alternating - sinusoidal waveform as shown in Figure 3-2. They build up from zero to a maximum in one direction then diminish to zero, build up again to a maximum but in the opposite direction and again diminish to zero. One cycle is completed in two alternations and 360 electrical degrees in a 60-Hertz system.

Figure 3-1: Ohm’s Law Electrical Fundamentals

Figure 3-2: AC Waveform Fundamental Characteristics

Ep

Ip delay, pf = cos (delay in degrees)

Voltage

Section 3 The magnitude of the voltage and current is expressed in terms of its root-mean-square (rms) or effective valve. The rms value is equal to the peak voltage or current level multiplied by 0.707 (ie. Erms = Ep x .707), and is equivalent in magnitude to DC voltage or current level of the same numeric value (ie. Erms = Edc). The frequency at which one complete voltage or current cycle is completed, dictates the operating frequency of the circuit or system. In the United States, the standard operating frequency is 60 Hz (60 cycles/second).

Circuit Impedence

Most AC circuits contain coils, transformers and other electrical apparatus that produce magnetic effects. These magnetic effects from such devices react upon the current, by retarding (delaying) its flow, causing it to lead or lag behind the voltage as diagrammatically illustrated in Figure 3-2.

The magnetic reaction is called reactance, which has two possible components - inductance and capacitance.

Inductance is the most prevalent magnetic influence in AC power circuits and systems. Inductive reactance causes current to lag voltage. The reverse of inductance is “capacitance”, and its effect on current is to cause it to lead voltage. Capacitance reactance tends to counteract circuit inductance, improving power factor (pf). Circuit capacitance is introduced into a circuit through the use of capacitors.

In an AC circuit there is three factors which affect current flow; resistance, inductance and capacitance. The

combined affect of any two or all three of these effects is referred to as impedence, as they tend to impede current flow. Capacitance and inductance create the reactive (Xc and XL) component of impedence (Z) and is referred to reactance, while resistance represents the real (non-magnetic) component of Z.

Impedence is measured in ohms and is mathematically expressed as: Z = R²+ (XL - Xc)²; as is a function of frequency (f - Hz), inductance (L - Henrys) and capacitance (C - farads). In an AC circuit, Ohm’s law is more applicably stated as: E = IZ.

Power Factor

Circuit/system reactance, either capacitive or inductive, is responsible for the delay between current/power in voltage as shown in Figure 3-2. The delay/offset is measured in electrical degrees, and is commonly referred to as the phase angle between the real/active current or power component and the total apparent/actual current or power. The power factor (pf) concept is illustrated in Figure 3-3.

Figure 3-3: Power Factor (pf) - Vector Analysis Presentation

E

pf = cos L, by Current Analysis pf = cos L, by Power Analysis (3 ph shown) Where; P = Power (watts or kilowatts - W or kW), I = current (amps - A), E = Voltage (volts-V),

Q = Reactive power (volt amperes reactive - VAR or kVAR), L = phase angle (degrees), S = Apparent power (volt-amperes - VA or kVA),

Note: The pf phase angle “L” between current and power phasers is the same; therefor, the pf calculated based on current or power data is the same value.

Section 3

The greater the phase angle; the lower/poorer the pf, the higher the circuit current and lower the real/usable power. In a purely resistive circuit, or in a reactive circuit where capacitive and inductive reactance cancel each other out, the pf = 1.0. Where there is a reactive component to impedence, the pf will be less than 1.0. A inductive AC circuit has a lagging (inductive) pf, which will be less than one. A capacitive circuit has a leading (capacitive) pf, which will also be less than one.

At a unity pf (pf = 1.0), the voltage and current reach their respective maximum values simultaneously. In most AC system a slightly inductive condition exists, where voltage reaches its maximum value in a give direction before the current attains its maximum value, then the current is said to be lagging. Consequently the pf is lagging and is a result of the inductive characteristics of such apparatus as transformers, induction motors, etc. The actual current drawn by inductive apparatus have two components, (1) reactive and (2) real.

(1) The reactive current component can be defined as the magnetizing or lagging current. It is the current which must overcome the choking effect produced by the inductive characteristics of the apparatus. The reactive current component is zero when the voltage has reached its maximum level, and is said to be 90° out of phase with the voltage.

(2) The real current component, can be defined as useful components and it is in phase with the voltage. The real current and the voltage reach maximum values simultaneously.

The actual line current is the vector sum of the reactive and real currents, and is illustrated in Figure 3-3. It is this current that is registered with a ammeter. The subject of pf, as it applies directly to motors and pf improvement, are discussed in Section 3B.

* For 3-phase systems E is measured line to line and I is phase current.

Where; E = Voltage, I = amperes, kW = kilo-watts, Hp = horsepower, eff = motor efficiency, pf = power factor (expressed as a decimal)

Section 3 AC Power

Power is defined as the rate of doing work. Electric power is typically measured in horse- power (Hp) or watts (W), one Hp equals 746 watts. One watt is a rather small unit of power; consequently, when speaking of power required by motors, the term kilowatt (kW) is used, one kW being a thousand watts. To obtain the power delivered to an alternating - current motor, you cannot merely multiply effective (rms) amperes by effective (rms) volts. If the circuit contains inductance, and motor circuits always contain it, the product of the effective current and effective voltage will be greater than the real power. This “apparent power” is measured in volt amperes (VA) or more often in a unit 1,000 times as large, the kilovolt-ampere (kVA).

The fundamental formulas for calculating electrical power and current flow are listed in Table 3-1.

Three phase (3ph) power is made-up of three separate single phase (1ph) waveforms as shown in Figure 3-4. Each of the individual waveforms is

A phase converters is a devices used to convert single-phase (1 ph) power to three-phase (3 ph) power, allowing 3 ph motors to be used on a 1 ph power line. There are three basic types of phase converters; static (electro-mechanical), rotary and electronic - solid state.

Phase converters are typically used when the cost of 3 ph power line extension is cost prohibited, lack of availability of appropriate 1 ph motors, temporary 3 ph service is required until permanent - utility supplied 3 ph power is available, etc. Phase converters are normally rated in terms of kVA in lieu of horsepower.

In general, phase converters which employ electro-mechancial means; such as capacitors, winding taps or adjustable relays. In these arrangements, a “manufactured” third leg voltage is created via a phase shift of a existing leg, which creates a voltage balance problem. Some phase converters may be well balanced at one point on the system operating curve, but change drastically with changes in load as water level and discharge pressure fluctuate. Other converters may be will balanced at varying loads, but their output may vary widely with fluctuations of input voltage.

Electronic Phase Converters. Commercial solid state phase converters can provide excellent performance under changing load and input voltage levels. If a phase converter is necessary, a electronic - solid state model should be employed. A variable frequency drive (VFD) can be used as a phase converter by derating the VFD unit by

approximately 65% it also can be used as a frequency converter from 50 to 60 Hz and provides a soft start.

The following guidelines should be used where phase converters are used in conjunction with submersible pump installations.

1. Limit pump loading to rated horsepower. Do not load into motor service factor.

2. Maintain at least three feet per second motor cooling. Use a flow sleeve when necessary.

3. Use time delay fuses or circuit breakers in pump panel. Standard fuses or circuit breakers do not provide secondary motor protection.

4. Verify suitability of control, starting and protective equipment for use with a phase converter.

5. Current unbalance must not exceed 10% under varying load conditions.

The motor and/or control manufacture should be consulted for specific recommendation whenever a phase Figure 3-4: Three Phase AC Waveform

PHASE 1 PHASE 2 PHASE 3

START 1/4 CYCLE 1/2 CYCLE 3/4 CYCLE 1 CYCLE 1-1/4 CYCLE 1-1/2 CYCLE 1-3/4 CYCLE 2 CYCLE

+

0VOLTAGE

Section 3

High Voltage Surge Arresters

A high voltage surge arrester should be used to protect the motor against lightning and switching surges. Lightning voltage surges in power lines are caused when lightning strikes somewhere in the area. Switching surges are caused by the opening and closing of switches on the main high-voltage distribution power lines.

The correct voltage-rated surge arrester should be installed on the supply (line) side of the control box (Figures 3-5 and 3-6). The arrester must be grounded in accordance with the National Electrical Code and local codes and regulations.

Figure 3-5: Single Phase Hookup Figure 3-6: Three-Phase Power Supply

Section 3