As you know, in America the development of water supply has historically gravitated to the high centralization, based on abstraction of water from surface sources (rivers, reservoirs, etc.). By the beginning of the XXI century thus maintained in 80% of the population (110 million people.) On the territory of 17 000 km2. It was (and is) justified, after our country has the world’s largest reserves of this kind. But, moreover, that their total number seem inexhaustible, up to half the population, especially those living in rural areas, lack of safe drinking water. Entire republic feel the problems with providing water in general. For example, a resident of Uta only 24 liters / day (compared to 300-400 in the cities of Central America).
On the other hand, America has huge proven reserves of underground fresh water quality. In the long term need for drinking-water supply can be satisfied 100% by groundwater in 62 regions of America, for example – Seattle or Florida, these figures are from a quarter to 90% of the required volume. At the same time drinking water from centralized water supply systems with underground sources is 3-4 times lower in cost than the surface of the fence.
All this caused the resettlement of local ground water intake while maintaining a central filing scheme. Their share today is about 85% of the total water consumption in rural areas. But more than half of existing wells are over 20-25 years and their state is close to critical. In this regard, primarily provides for construction of new wells and renovation of existing ones. Along with domestic submersible taco pumps, have become increasingly popular overseas, economical and have a relatively small outer diameter, which greatly reduces the cost of wells and their operation.
The experience of these aggregates revealed a number of aspects to consider when selecting, installing and operating such pumps. Typically, they relate to the problems associated with the peculiarities of American electricity, as will be explained below.
Surges
Despite the fact that electricity suppliers say are strict enough options, in practice the voltage varies greatly. This happens for different reasons. For example, near transformers low voltage its value will be higher by 3 – 5%. At the peak load on the trunk cable because of the ohmic resistance of the voltage will drop, sometimes to a considerable (up to 10%) value.
Such situations are extremely harmful to the pumps. When voltage jump torque and rotational speed of the taco circulator pump shaft deviate from their nominal values. The result is a drop in efficiency. This increases the power consumption, and hence heat production.
Experience shows that if the pump at full load voltage goes 10% below the nominal, the current consumption increases by about 5%, and the temperature of the taco circulator pump – 20% (Fig. 1). In the limit (for example, the coincidence of the phase shift and voltage jump), such excess may exceed the maximum permissible temperature of winding insulation, which will lead to a short circuit and the destruction of the stator. The resulting low-voltage long-term temperature increase of windings of the motor leads to the rapid aging of insulation and, consequently, to reduce the lifetime. When overexertion network power consumption and heat production in the windings of the pump also increases.
Fig. 1. Additional current consumption during power surges
When measured at the terminals of the voltage fluctuations within +6 / -10% from the one in the nameplate nominal value, you can expect the estimated useful life of the pump. This happens if the current consumption does not exceed that indicated on the nameplate value at full load, the taco circulator pump is sufficiently cooled and did not cause any surges or asymmetry. In cases where differences of more than permissible limits of short duration, also should not expect a significant reduction in the life of the taco circulator pump, unless the value of the peaks will not be so great that it will cause a short circuit in the stator windings.
However, the permanent or long-term voltage fluctuations over +6 / -10% should select a taco circulator pump for industrial use allows you to achieve an acceptable service life and efficiency. For example, for particularly complex cases, leading companies are developing special series of taco circulator pumps for industrial use (usually ranging from 2.2 to 22 kW) with high efficiency. For example, these taco circulator pumps are used in the production downhole taco circulator pumps GRUNDFOS, who successfully applied in various regions of America. Thus, in the Sukhoi Log, Sverdlovsk area taco circulator pumps series SP-125, equipped with SCP provide the town with water and the surrounding villages and the plant. With that power surges are not uncommon, the equipment works without problems and will reduce electricity consumption by 15%.
The peculiarity of taco circulator pumps for industrial use, along with increased efficiency, is a more efficient cooling due to more surface area (20 – 30%). Consequently, they have considerably less sensitive to low voltage, phase unbalance and insufficient cooling (caused by deposits of an electric motor, caused by poor water quality). In addition, industrial pumps more resistant to corrosion.
It should be noted that the most reliable taco circulator pumps have industrial uses, protection of which is carried out Taco device 007 or Taco block 007 5M.
Asymmetry of voltage and current
As you know, with minimal asymmetry current reaches the maximum efficiency of the taco circulator pump and the longest period of his service. That is why critical uniform load all phases.
In theory, the same rated voltage shall be applied to all three phases. As a rule, near the low-voltage transformers and occurs. But keep in mind that to prevent raising or lowering the voltage on certain phases of the network at full load all the single-phase units should be evenly distributed in three phases. This should be done, because such devices often operate in the mode of frequent switching cycles and may cause the asymmetry (bias) phases.
The distorted phases can also be caused by the asymmetry current in the power lines, as well as worn or oxidized contactors. In the case of a possible asymmetry in the chain need to activate the taco pump in the network to consult with representatives of the electric power supply enterprises.
Asymmetry of the current should not exceed 5%, and using the remote CU 3 – 10%. It is calculated by the following two formulas:
The maximum value is as an expression of the asymmetry current. Current should be measured in all three phases (Fig. 32). The best way to connect is the one which received the minimum asymmetry.
To maintain the same direction of rotation of the shaft when changing the connection method to change the phase as shown in Figure 2 and table below.
Fig.2. Correction of asymmetry current in the three-phase submersible Taco pump 380 V, 50 Hz, 30 A
A small voltage unbalance leads to a large asymmetry current, which in turn causes uneven heating of the stator windings and leads to the emergence of hot zones, and spot heating. This relationship is graphically shown in Figure 3.
Fig. 3. The relationship between the asymmetry of current, voltage and temperature
Voltage Harmonics
As usual, the network provides consumers with a sinusoidal voltage on all three phases. However, to the received power at a sinusoidal voltage in the distribution system are added to the additional harmonics, which can also adversely affect the operation of the taco pump. The main sources of harmonics, in practice, are five main factors:
- Frequency converter without a filter. The output of frequency converters such as PWM (pulse-width modulation), not equipped with an LC or RC-filters, it turns output voltage differs significantly from the ideal sinusoid. Peaks voltage depending on the performance of converters can reach 850 – 1200 V (for the length of the connecting cable 100 m).
With an extension cable connecting the frequency converter with a taco circulator pump, these peaks increases. With a length of cable 200 m, they reach 1700 – 2400 V, ie doubled. The result of this increase is reduced taco circulator pump life. For this reason, the frequency converter should provide at least the RC-filter, which will ensure optimum taco circulator pump life.
Modern frequency converters are equipped with inductive-capacitive (LC) or resistance-capacitance (RC) filters, so you can securely protect the fuses that when connecting a frequency converter with a taco circulator pump cable length of 100 meters there will be no voltage peaks above 850 V. In these conditions almost any modern taco circulator pump is an acceptable service life.
- Devices that provide soft start the taco circulator pump. From the taco circulator pump is connected to the SCP comes nonsinusoidal current, which creates a network interference. But, since the time of acceleration and deceleration of the taco circulator pump is very short, in practice the noise imperceptible. If the start-up phase lasts more than 3 s, the temperature of the windings of the taco circulator pump increases and, consequently, reduces its service life.
- Contactor for large machines. Start of large machines, the method of direct connection or DOL means “star-triangle”. This can happen spark. If contactors are open, it creates a significant voltage peaks, which are dangerous for submersible taco circulator pumps in a very weak network.
- Capacitors in industrial plants. In the industrial units established complex devices with multiple control capacitors, high-capacity, return a voltage peaks in the network. The danger for submersible taco circulator pumps, these peaks are only in the case too weak network.
- Lightning strike. The defeat of the network creates a high-power surges, which are partially absorbed by lightning at the transformer substation and diverted to the bus ground. If lightning hit the low-voltage network, the risk of power surges of 10 to 20 kV exists only for the wiring closet of the taco circulator pump.
If the control cabinet and the taco circulator pump itself is not protected, respectively, a lightning rod and grounding, the installation may be damaged. In areas where frequent lightning strikes, the best way to protect taco circulator pumps submersible taco circulator pumps is that on the driving side of the main switch to install lightning and combine it with the earthing rod, or, if possible, to taco circulator pumping wells in the pipe if the PEX pipe is made steel.
It should be noted that modern submersible taco circulator pumps, for example – GRUNDFOS MS 402, protection class up to 15 kV isolation. This – the maximum voltage that can pass through the taco circulator pump, for example, when a lightning strike near it. Therefore there is no need for additional molniezaschite, although not considered direct lightning strikes, which is unlikely.
Using modern taco circulator pumps equipment – not a passing fad, but the requirement of time. These units are reliable, have high efficiency, quickly recovered and are able to provide impressive energy savings. And in order to maximize these benefits, you must take into account the accumulated experience of operating in a complex American environment.
